question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>I came across a problem which reads: </p>
<blockquote>
<p>The speed distribution function of a group of <em>N</em> particles is given by:<br>
$dN_v = kv\; dv\; (V>v>0)$<br>
$dN_v = 0 \; (v>V) $<br>
(a) Draw a graph of the distribution function.<br>
(b) Find the constant <em>k</em>... | 2,721 |
<p>I am reading Pekar's "Research in Electron Theory of Crystals" and I came across a passage I find a bit unclear:</p>
<blockquote>
<p>The theory developed below takes into account the dielectric
polarization of a an ionic crystal by the electric field of the
conduction electron. The local polarization that res... | 2,722 |
<p>My question is in two parts. </p>
<ol>
<li><p>What is the origin of the electric field from an electric charge and why electron can have so small mass? While on the other hand for a magnetic monopole to create a magnetic field needs to be so heavy? </p></li>
<li><p>And if the magnetic monopole is a hadron what are ... | 2,723 |
<p>I've observed this behavior many times. When it rains, the rainwater will form vertical channels along a glass window. The flow of water is mostly confined within these vertical channels and the channels are (more or less) stable.</p>
<p>But sometimes - and I suspect this happens when the flow intensity in one of t... | 2,724 |
<p>In Zurek's theory of quantum Darwinism, information about the pointer states of a system imprint themselves upon fragments of the environment carrying records about the state of the system. Multipartite entanglement between the system and the many fragments effectively become classical correlations whenever one does... | 2,725 |
<p>Reading Dirac's Principles of Quantum Mechanics, I encounter in § 36 (Properties of angular momentum) this fragment:</p>
<p><img src="http://i.stack.imgur.com/z9T4O.png" alt="enter image description here"></p>
<p>This is for a dynamical system with two angular momenta $\mathbf{m}_1$ and $\mathbf{m}_2$ that commute... | 2,726 |
<p>I've come across this explanation that the "arrow of time" is a consequence of the second law of thermodynamics, which says that the entropy of an isolated system is always increasing. The argument is that the past looks different from the future because of this increase in entropy. However, this still doesn't make ... | 2,727 |
<p>How Dielectrics as an Insulating materials transmit electric effect without Conducting Electricity ? How its Possible ??</p> | 2,728 |
<p>OK I know that <strong>R= V/I</strong>. I also know that <strong>R = ρl / A</strong> But what I want to know is that what really causes resistance? Is resistance equivalent to force? or is it just a constant?</p>
<p>Also, what causes conductors to heat up overtime when current flows through them? I know that the el... | 2,729 |
<p>What's the most fundamental definition of <a href="http://en.wikipedia.org/wiki/Temperature" rel="nofollow">temperature</a>? Is it the definition concern about average energy, number of micro states, or what?</p>
<p>By "fundamental", I mean "to be applied" in such general cases as Black Hole's Temperature, Accelera... | 2,730 |
<p>I have a wheel (free to spin around the $z-$axis) with four spokes that is connected by sliding contacts to a circuit with $U_0 = 0,72V$. Also, there is a B-Field parallel to the $z-$axis
<img src="http://i.imgur.com/aLF3N7S.jpg" alt="Imgur"></p>
<p>For the induced electric potential I have:
$$U_i = - \frac{1}{2}(R... | 2,731 |
<p>In this picture the acceleration vector $\vec{a}$ points upward when the pendulum is halfway</p>
<p><a href="http://en.wikipedia.org/wiki/File:Oscillating_pendulum.gif" rel="nofollow">Click To see animated GIF</a></p>
<p>But according to this picture, the force acts tangentially:</p>
<p><img src="http://i.stack.i... | 2,732 |
<p>I need to determine angular velocity of a disc when a man with given mass and speed whacks on the edge of it. </p>
<p>I calculated the total moment of inertia of disc and body, how do I calculate the angular velocity of the disc? ( radius and mass of the disc are also given ).</p> | 55 |
<p>When physicists talk about the expanding universe they often say that the distant galaxies are not really "moving" away but instead the space itself between us and them is expanding. If this is true then the expansion should apply to every region of space proportionally. Coming from a different direction, we all kno... | 56 |
<p>Do sound waves in a gas consist of phonons?</p>
<p>What about a glass? Or other non-crystalline materials such as quasicrystals?</p>
<p>How does the lack of translational symmetry affect the quantization of the displacement field?</p>
<p>All the answers so far have treated this question at a much more elementary ... | 2,733 |
<p>How to find velocity and displacement equations from a given force equation? For instance, it was given the following 1-D equation:</p>
<p>$$F = b_1(v_1-v) - b_2 v$$</p>
<p>$v_1$, $b_1$ and $b_2$ are constants.</p>
<p>I know that $F = ma = m\frac{\mathrm{d}v}{\mathrm{d}t}$, but I can't find how to integrate $F$. ... | 2,734 |
<p>Is there any good reference for conceptual problems for students which learn nuclear physics first time? I am not searching problems that involve difficult calculations. Quite the converse, they should be computational rather simple but conceptually difficult. </p> | 2,735 |
<p>According to the reports, the shutdown procedures at all the Fukushima reactors were successful, and all the control rods were fully inserted.</p>
<p>So - if there was a meltdown, would the control rods also melt and blend into the resulting material (corium)? If so, would that have the effect of "diluting" the cor... | 2,736 |
<p>I've seen the claim that solar eclipses are more common in the southern hemisphere than the northern hemisphere and would like to understand why and if that is the case? Does it relate more to the position of the moon relative to the earth or more to how the earth rotates the sun or is this just hogwash?</p>
<bloc... | 2,737 |
<p>Turns out there's <a href="http://en.wikipedia.org/wiki/Tritium_illumination" rel="nofollow">tritium illumination</a> - a tiny very strong plastic tube will be covered in phosphor and filled with tritium. Tritium will undergo beta decay and a flow of electrons will cause the phosphor to glow.</p>
<p>This gives enou... | 2,738 |
<p>With Hawking radiation, one half of virtual pair falls into horizon and this particle has negative energy.</p>
<p>What would an observer inside horizon observe when seeing negative particles ?
How do these negative particles interact with ordinary matter ?</p> | 2,739 |
<p>Space looks like time depending on the motion of the observer so I was going to ask if space expansion was the same as the unfolding of time, but this was asked on physics.stackexchange <a href="http://physics.stackexchange.com/questions/32494/the-expansion-of-space-time-est-and-the-one-directional-flow-of-time">bef... | 26 |
<p><img src="http://i.stack.imgur.com/Bt418.png" alt="enter image description here"></p>
<p>I wonder how can I prove the fulfillment of the third principle of Nernst of a body that obeys the next expression.</p> | 2,740 |
<p>I think, the answer is probably yes, but it can be answered by somebody who knows GR much better than I do.</p>
<p>In case of a positive answer, can we say that gravitational radiation will be bent around graviting bodies exactly as light?</p> | 2,741 |
<p>As far as I know, most of an atom is vacuum. </p>
<p>Therefore, in theory, would it be possible for me to throw a tiny stone through my window without breaking it because no matter actually collides?</p> | 2,742 |
<p>What does change in magnetic flux mean? How can you change magnetic flux? How does a change in magnetic flux influence a current of electrons (electricity)? </p> | 2,743 |
<p>Let's say that an observer is moving with the speed of light relatively to an atom that he wants to look into. He has equipment that precise that he can observe the atom and what is inside.</p>
<p>From Einstein's theory we know that for light particles, everything else that moves with velocity smaller than the spee... | 2,744 |
<p>In a basic friction problem with Block A sliding on top of Block B, the direction of the friction force is usually explained as being simply the opposite of the direction of motion. So if Block A is sliding to the right, the friction force is pointing to the left. But this reasoning implicitly assumes that we are ca... | 2,745 |
<p>The <a href="http://en.wikipedia.org/wiki/Large_Underground_Xenon_Detector">Large Underground Xenon Detector</a> (LUX) recently released results<sup>1</sup> that they have found no signs of dark matter<sup>2</sup> after a ~3 month search this spring and summer. The LUX group plans to spend all of 2014 looking for da... | 2,746 |
<p>I need some books to learn the basis of linear operator theory and the spectral theory with, if it's possible, physics application to quantum mechanics. Can somebody help me?</p> | 2,747 |
<p>I read Arnold's book <strong>Mathematical Methods of Classical Mechanics</strong> and come across with <a href="http://books.google.com.hk/books?id=Pd8-s6rOt_cC&pg=PA229&lpg=PA229&dq=be+simple+%28multiplicity+1%29+eigenvalues+of+a+symplectic+transformation&source=bl&ots=uKsjzFCKMv&sig=hZCx5PX... | 2,748 |
<ol>
<li><p>What's the motivation behind the action principle?</p></li>
<li><p>Why does the action principle lead to Newtonian law? </p></li>
<li><p>If Newton's law of motion is more fundamental so why doesn't one derive Lagrangians and Hamilton principle from it? </p></li>
<li><p>Also does all Lagrangians obey $L=T-V$... | 2,749 |
<p>I can't understand the electrolytic capacitors, when a capacitor has a capacitance of 100 microfarads, does that mean that when it is charged with 100 volts will the charge of the plate be 0.01 coulomb? If there is a part of the plate with no isolation, then I touch it, I will be shocked with a charge of 0.01 coul... | 2,750 |
<p>Is it true that $\left(H^\dagger H\right)^2$ is invariant under $U\left(1\right) \times SU\left(2\right)$ where $H$ is the Higgs field $(1,2,1/2)$?</p>
<p>Does this invariance imply that its hypercharge is invariant under $U\left(1\right)$ and its spin is invariant under $SU\left(2\right)$? . </p>
<p>$$H = [H... | 2,751 |
<p>A few closely related questions regarding the physical interpretation of the S-matrix in QFT: I am interested in both heuristic and mathematically precise answers.</p>
<p>Given a quantum field theory when can you define an S-matrix? Given an S-matrix when can you define a quantum field theory from it? (e.g. I have ... | 2,752 |
<p>Assuming we have a sufficiently small and massive object such that it's escape velocity is greater than the speed of light, isn't this a black hole? It has an event horizon that light cannot escape, time freezes at this event horizon, etc. However this object is not a singularity.</p>
<p>If a large star's mass were... | 2,753 |
<p>In condensed matter literature, at many places, the phrase 'deep lattice limit' is used. Please tell what is the <a href="http://www.google.com/search?q=%22deep+lattice+limit%22" rel="nofollow">deep lattice limit</a> and the <a href="http://www.google.com/search?q=%22shallow+lattice+limit%22" rel="nofollow">shallow ... | 2,754 |
<p>In a well known Maxwell paper he uses the units of wavelength which he calls the Fraunhofer Measure. He states it for the Fraunhofer D and F bands as</p>
<p>$$\lambda_D = 2175 \text{ crazy units} = 589nm$$</p>
<p>$$\lambda_F = 1794 \text{ crazy units} = 486nm$$</p>
<p>So the conversion is:</p>
<p>$$1nm \approx 3... | 2,755 |
<p>It is often quoted that the number of atoms in the universe is 10$^{70}$ or 10$^{80}$.</p>
<p>How do scientists determine this number? </p>
<p>And how <em>accurate</em> is it (how strong is the supporting evidences for it)?</p>
<p>Is it more likely (logically >50% chance) that the numbers are right, or is it more... | 846 |
<p>As suggested by one of the commentators on my <a href="http://physics.stackexchange.com/questions/47713/the-story-since-bohr">last question</a>, I am going through Bohr's Nobel prize lecture in order to understand how quantum mechanics was developed. </p>
<p>The lecture describes Planck's observations on radiations... | 2,756 |
<p>In <a href="http://profmattstrassler.com/2012/12/21/its-not-the-end-of-the-world/" rel="nofollow">this</a> end of the year article, Prof. Strassler mentioned that hidden valley sectors could lead to some still open loopholes concerning the experimental discovery of supersymmetry and other BSM physics at the LHC such... | 2,757 |
<p>I'm and undergraduate student and I'm doing a report on Quantum computing. As a conclusion of my report I'd like to highlight the latest experimental advances in Quantum Computing, especially in methods like Ion trap and photon polarization. Most of the study I've made is on papers and documents dated 2000 or earlie... | 2,758 |
<p>I'm looking at the 1927 paper of Thomas, The Kinematics of an Electron with an Axis, where he shows that the instantaneous co-moving frame of an accelerating electron rotates and moves with some infinitesimal velocity. He states:</p>
<blockquote>
<p>At $t=t_0$ let the electron have position $\mathbf{r}_0$ and vel... | 2,759 |
<p>Where can one find old Russian scientific papers in physics, say, in the Proceedings of the Russian Academy of Sciences or Zhurnal Eksperimentalnoy i Teoreticheskoy Fiziki? Can they be found online somewhere?</p> | 2,760 |
<p>According to relativity,nothing can break light barrier.But a recent <a href="http://arxiv.org/abs/1101.1840" rel="nofollow">preprint</a> shows energy transmission of commercial electric power (f=60Hz) is faster than light. (It is not the drift velocity of electrons because energy transport depends on the electromag... | 2,761 |
<p>This is a thought I had a while ago, and I was wondering if it was satisfactory as a physicist's proof of the positive mass theorem.</p>
<p>The positive mass theorem was proven by Schoen and Yau using complicated methods that don't work in 8 dimensions or more, and by Witten using other complicated methods that don... | 2,762 |
<p>A tennis player has a tennis ball container with a single ball in it (it normally holds three). He shakes the tennis ball horizontally back and forth, so that the ball bounces between the two ends. We model the tennis ball as a quantum particle in a box.</p>
<p>The questions: what is the quantum number n for this b... | 2,763 |
<p>One way to normalize the free particle wave function </p>
<blockquote>
<p>"is to replace the the boundary condition $\psi(\pm{\frac{a}{2}}) = 0$ [for the infinite well] by periodic boundary conditions expressed in the form $\psi(x)=\psi(x+a)$"
-- <em>Quantum Physics</em>, S. Gasiorowicz</p>
</blockquote>
<p>H... | 2,764 |
<p>The edge of a fractional quantum Hall state is an example of a chiral Luttinger liquid. Take, for the sake of simplicity, the edge of the Laughlin state. The Hamiltonian is:</p>
<p>$$H = \frac{2\pi}{\nu}\frac{v_c}{2} \int_{\textrm{edge}} dx \rho(x)^2 $$</p>
<p>Here $\nu$ is the filling fraction, which is constant,... | 2,765 |
<p>So I am studying for a final and can't seem to solve this. There is a log floating in water and I need to find its weight. The question I have is what parts of the volume of the log count when summing the forces in the Y axis.</p>
<p><img src="http://i.stack.imgur.com/108N2.png" alt="enter image description here"><... | 2,766 |
<p>I am seeking an algorithm to generate a random wavefunction = $\sum {c_i |\varphi _i\rangle }$ from a thermal ensemble, whose density matrix $\rho \sim e^{-\beta H}$, without the need to diagonalize the Hamiltonian. One possible method is to generate a random number for each basis and compare it with $e^{-\beta \lan... | 2,767 |
<p>When one is doing zeta-function regularization of the heat-kernel for QFT then one is doing these following steps,</p>
<ul>
<li>the integral over the imaginary time</li>
<li>taking the trace of the heat-kernel or the short-distance limit </li>
<li>the space-time volume integral</li>
</ul>
<p>I would like to know a... | 2,768 |
<p>I'm a first year physics student and the main source for our Physics I course is "Berkeley Physics Course - Volume I."
I'm having a hard time understanding this book because it assumes a pretty high level of previous knowledge, and the mathematical level is also advanced. </p>
<p>Is anyone familiar with a site tha... | 2,769 |
<p>Magnetic fields are obvious distortions.. of.. something, but what exactly are they distortions of? Massive objects produce curvatures/gradients in space-time resulting in what we observe as gravity.. what is the equivalent explanation for magnetic/electric fields?</p> | 2,770 |
<p>I require only a simple answer. One sentence is enough... (It's for high school physics)</p> | 2,771 |
<p>Seeing an interesting BBC article today at <a href="http://www.bbc.co.uk/news/science-environment-23514521" rel="nofollow">http://www.bbc.co.uk/news/science-environment-23514521</a> about the Longitude Problem, I wondered if it could have been solved, in a way practical at the time (the 18th century), by any means o... | 2,772 |
<p>I learned electrodynamics.
According to the vector potential determination,
$$
\mathbf B = [\nabla \times \mathbf A ],
$$
Coulomb gauge,
$$
\nabla \mathbf A = 0,
$$
and one of Maxwell's equations,
$$
[\nabla \times \mathbf B ] = \frac{1}{c}4\pi \mathbf j,
$$</p>
<p>I can assume, that</p>
<p>$$
[\nabla \times \mat... | 2,773 |
<p>I am a postgraduate in mathematics. I studied physics during my B.Sc.studies.I want to go for further studies in physics particularly in theoretical physics. I am in a job and cant afford regular classroom teaching. Could anyone tell me something about some distance education programs? or are there programs for math... | 2,774 |
<p>The theory of an anti-reflective coating is that the reflected light off the coating and the reflected light off the substrate is 180 degrees out of phase, causing destructive interference and subsequently no light is 'reflected'. But how does this process allow more light to pass through the substrate. Because alth... | 2,775 |
<p>Why is the force required to slide a magnet off a steel plate A LOT less than the force required to directly pull it off?</p>
<p>The force required to pull the magnet can be: 20lb
While the force required to slide the magnet can be: 1lb more/less.</p>
<p>Why is that?</p> | 2,776 |
<p>I refer to the time-domain version of the Poyinting theorem in electro-magnetism:</p>
<p>$- \displaystyle \oint_S (\mathbf{E} \times \mathbf{H}) \cdot d\mathbf{S} - \int_V \mathbf{E} \cdot \mathbf{J}_i \ dV = \int_V \frac{\partial}{\partial t} \frac{\mu |\mathbf{H}|^2}{2} \ dV + \int_V \frac{\partial}{\partial t} \... | 2,777 |
<p>I have calculated a tree level amplitude for Compton scattering (${e\left(p\right)+\gamma\left(k\right)\to e\left(p\prime\right)+\gamma\left(k\prime\right)}$):</p>
<p>$${
i\mathcal{M}=M_{\mu\nu}\epsilon^{*\mu}\left(k\prime\right)\epsilon^{\nu}\left(k\right)\textrm{.}
}$$</p>
<p>How should I go about trying to veri... | 2,778 |
<p>I get water to my home from a nearby Tank A at a certain height above ground level.
I have a 1" pipe through which I get this water to my home.. I leave this water into my well by connecting a 1" tube to this pipe. </p>
<p>Reason for question: I have seen water pressure vary(lower- more flow) depending upon the hei... | 2,779 |
<p>Can we get high energy from laser like fusion and fission reactions ? what is highest energy we can get from laser ?</p> | 2,780 |
<p>Title says it all.</p>
<p>Have they been seen in experiment or are they just theoretical things?</p>
<p>Do quarks really exist?</p> | 2,781 |
<p>I was wondering whether there is an equation that enables me to calculate the reflection, transmission, absorption and polarization, when the electric field everywhere is given?</p>
<p>Consider this: You have solved the full Mie scattering process, so incident field, the field in the sphere and the scattered field ... | 2,782 |
<p>Even on a current new 2012 car, when the green LED clock inside the car is quite bright, but when the car's headlight is turned on, the clock dims down to only about 1/4 of its brightness, which makes the time hard to see.</p>
<p>I thought the clock requires merely a watt or even less for its brightness, and the ca... | 2,783 |
<p><strong>The situation</strong></p>
<p>An inclined conveyor belt with topmost point $h$ height above the ground receives sand at a constant rate $X$ from a container at a negligible height above the lowermost point of the conveyor belt. There is sufficient friction on the conveyor belt so that the sand stops almost ... | 2,784 |
<p>EDIT: I think I can pinpoint my confusion a bit better. Here comes my updated question (I'm not sure what the standard way of doing things is - please let me know if I should delete the old version). The major change is that I removed focus from the third question which probably is a purely mathematical question (in... | 2,785 |
<p>I've been wondering about the porosity of materials, I know that, for example the air comes out of tires/balloons because (besides having huge gaps on the rim contact area/knot) they are made of a porous material, but it has nothing to do with molecules, because the porosity appears in a much larger scale.</p>
<p>N... | 2,786 |
<p>Consider a solid ball of radius $r$ and mass $m$ rolling without slipping in a hemispherical bowl of radius $R$ (simple back and forth motion). Now, I assume the oscillations are small and so the small angle approximation holds. I wish to find the period of oscillation and I analyze the motion in two ways, first usi... | 2,787 |
<p>What is the relationship of <a href="http://en.wikipedia.org/wiki/General_relativity" rel="nofollow">General Relativity</a> and <a href="http://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation" rel="nofollow">Newtonian</a> <a href="http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion" rel="nofollow">M... | 2,788 |
<p>Consider a system of particles where the kinetic energy of the system is varying with time. I'd like to know the significance (or meaning) of the time derivative of the kinetic energy being zero at a point. What is the significance of time instances where the kinetic energy has maxima and minima ?</p> | 2,789 |
<p>Someone once incorrectly told me that, given the speed of light is the speed limit of the universe, aliens would have to live for hundreds of years if they are to travel distances of hundreds of light years to reach Earth.</p>
<p>In a "special relativistic" and non-expanding universe however, this is not the case. ... | 2,790 |
<p>Notation: The magnetic field $\mathbf{B}$ generated by a point charge $e$ moving with velocity $\mathbf{v}$ is given by <a href="http://en.wikipedia.org/wiki/Biot%E2%80%93Savart_law" rel="nofollow">Biot-Savart's law</a></p>
<p>$$\mathbf{B} = \frac{\mu_0 e\ \mathbf{v} \wedge \mathbf{r}}{4\pi r^3}$$ where $\mathbf{r}... | 2,791 |
<p>Some time ago I asked a question about gravity on a hemispherical planet.</p>
<p><a href="http://physics.stackexchange.com/questions/29707/what-would-gravity-be-like-on-a-hemispherical-planet">What would gravity be like on a hemispherical planet?</a></p>
<p>Would the water all boil away at first, quickly cooling t... | 2,792 |
<p>I'm trying to model a flexible stick with a partial differential equation. I want one of the ends to be fixed and the other end to swing. </p>
<p>Do you guys know of any good models I can use? Any references would be appreciated. </p> | 2,793 |
<p>Just what the title states with the qualification that the change must be affected without using other celestial bodies as mentioned in the Clarke/Baxter SF 'Sunstorm'.</p>
<p>Obviously given the momentum of Earth it would require a major something to break the inertia. But something like the way an ice-skater whil... | 2,794 |
<blockquote>
<p><em>One charge density surface is distributed uniformly in one infinity tape of length with $2a$ width from distance $d$. Determine the Electric Field in the point perpendicular from the distance $d$ of the centre of tape.</em></p>
</blockquote>
<p>Answer: </p>
<blockquote>
<p>$\frac{\rho_s}{\pi\... | 2,795 |
<p>I have been told all my physics life that potential energy between two mass/charge has no meaning and only their difference has meaning. The same goes for electric potential, only the difference matter.</p>
<p>Perhaps I am not understanding it correctly, but before I talk about masses, let's talk about potential en... | 2,796 |
<p>Consider an ensemble of electrons which all experienced a collision at time $t=0$. Let $n(t)$ denote the number of electrons in this ensemble. </p>
<p>Assume that the number of electrons $\mathrm{d}n$ from this ensemble experiencing collisions in a time $\mathrm{d}t$ is proportional to $n$, i.e. $$\mathrm d n = -an... | 2,797 |
<p>Conductivity is noted in S.cm-1 in this <a href="http://pubs.acs.org/doi/abs/10.1021/ja502765n" rel="nofollow">http://pubs.acs.org/doi/abs/10.1021/ja502765n</a></p>
<p>i wanted to compare it to the conductivity values listed on wikipedia for common materials.</p>
<p>i could not find information on what the differe... | 2,798 |
<p>My problem gives me a Carnot cycle heat engine with water as its working fluid, with $T_H$, $T_L$, and the fact that it starts from saturated liquid to saturated vapor in the heating process.</p>
<p>I need to find the net work output of this engine. So my solution goes like this:</p>
<p>$$\eta_{HE} = 1 - \frac {T_... | 2,799 |
<p>I was watching a whip crack in slow motion and I noticed that the motion of the whip could be described using two different circular descriptions.</p>
<p>1) the user circles the whip around over his head, creating a rotation with a period.</p>
<p>2) next, he jerks the whip, causing a different and faster movement ... | 2,800 |
<p>In this <a href="http://www.mso.anu.edu.au/~charley/papers/LineweaverDavisSciAm.pdf" rel="nofollow">article</a>, the authors make the claim (pg <strong>44</strong>) that "Expansion by itself—that is, a coasting expansion neither accelerating nor decelerating—produces no force."</p>
<p>I'm having a hard time convinc... | 2,801 |
<p>I apologize if this question is dumb, but I've looked all over for a straightforward answer and either I can't find one or the terms are too complex for me to understand. I have only a rudimentary knowledge of Mechanics, but I do understand basic Linear Algebra.</p>
<p>So torque, mathematically, is the cross produc... | 413 |
<p>I am studying the <a href="http://en.wikipedia.org/wiki/M%C3%B8ller_scattering" rel="nofollow">Møller scattering</a>, but I don't know how to get the twisted diagram from the S-matrix. Has anybody a good explanation?</p> | 2,802 |
<p>If you unfold a tesseract into 3D space you get a cross shape (basically). <a href="http://www.youtube.com/watch?v=249AxWw-RbE" rel="nofollow">Animated</a>, it looks like the bottom most cube becomes inverted from it's 4D orientation. Would that mean that the pull of gravity within that cell would be opposite of the... | 2,803 |
<p>In the following circuit, I'd like to calculate the potential difference $V_{BA}$.</p>
<p>One way is to solve the circuit, by calculating all the currents $I_1, I_2, I_3$. The system of equations is:</p>
<p>$\{I_1 + I_2+I_3 = 0, 6 - 2 I_2 +2 I_1=0, 12 - 2I_3 + 2I_2 = 0\}$.</p>
<p>The solution is $(I_1, I_2, I_3) ... | 2,804 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/30824/can-a-photon-be-made-to-orbit-a-known-or-undiscovered-theoretical-body">Can a photon be made to orbit a known (or undiscovered theoretical) body?</a> </p>
</blockquote>
<p>How massive would a black... | 57 |
<p>Just as the title asks,</p>
<p>How far away can, say, a satellite be and still be in "orbit" ?</p>
<p>How about for a given velocity?</p>
<p><em>Fun Facts</em></p>
<p>200 miles (320 km) up is about the minimum to avoid atmospheric interference. The Hubble space telescope orbits at an altitude of 380 miles (600 k... | 2,805 |
<p>The force carrier for magnetic fields and electric fields are supposedly <a href="http://physics.stackexchange.com/questions/3134/is-the-force-carrier-of-the-magnetism-in-a-common-household-magnet-a-photon">photons</a>. I don't get it:</p>
<p>1) Wouldn't that mean that a charged particle (e.g. an electron or even ... | 2,806 |
<p>I've have got some vertical and horizontal distances for a projectile-like motion.</p>
<p>In order to work out the trajectory, why is it better to plot on the x-axis, "horizontal distance^2", and on the y axis, "vertical distance"?</p> | 2,807 |
<p>I am studying to return to school in physics and would like to start spending as much time as possible on that task. Most of my small amount of free time, however, I am either doing house work or commuting to work. While it is difficult or impossible to read while doing these chores, I think I could get great bene... | 522 |
<p>I'm currently learning what electromotive force is and while reading my book's description of an ideal source of emf, I had difficulty understanding what these sentences mean:</p>
<blockquote>
<p>The nonelectrostatic force maintains the potential difference between the terminals. If it were not present, charge wo... | 2,808 |
<p>I have a problem with the argument of a finite square well.</p>
<p><img src="http://i.stack.imgur.com/HVL3H.png" alt="enter image description here">
<img src="http://i.stack.imgur.com/O1rSN.png" alt="enter image description here"></p>
<p>The stuff I read has mentioned that the Curvature " second derivative " is op... | 2,809 |
<p>So here is my homework question: </p>
<blockquote>
<p><em>Two long cylindrical shells of metal (radii $r_1$ and $r_2$, $r_2 > r_1$) are arranged coaxially. The plates are maintained at the potential difference $\Delta\phi$. The region between the shells is filled with a medium of conductivity $g$. Use Ohm's la... | 2,810 |
<p>What does it mean by an infinite square well being <strong>transparent</strong>?
I have been doing the calculation of the infinite square well and I came up with an answer
$T = 1$ where
$T$ for Transmission coefficient.
But I can't really tell what it actually means in terms of physics.
I would imagine a particle to... | 2,811 |
<p>I have a pretty basic pulley problem where I lack the right start.</p>
<p>A child sits on a seat which is held by a rope going to a cable roll (attached to a tree) and back into the kid's hands.</p>
<p><img src="http://wstaw.org/m/2011/11/08/m7.png" alt="Sketch"></p>
<p>When it sits still, I believe that the forc... | 502 |
<p>Did Einstein completely prove Newton wrong? If so, why we apply Newtonian mechanics even today? Because Newton said that time is absolute and Einstein suggested it <a href="http://en.wikipedia.org/wiki/Theory_of_relativity" rel="nofollow">relative</a>? </p>
<p>So, if fundamentals are conflicting, how can both of th... | 2,812 |
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