question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>If a spring is cut up into n pieces, does the spring constant also change for these cut pieces?
I know spring constant is inversely proportional to deformation but is the same true for even the true length of the spring?</p> | 194 |
<p>Suppose we have a finite , discrete set of orthonormal states $|k\rangle $</p>
<p>We can construct raising and lowering operators intuitively, for example $$a_+ =\sum_{k=1}^nC_{k+1}|k+1\rangle \langle k|$$</p>
<p>However most textbooks begin by defining ladders in terms of the linear combinations of hermitian oper... | 5,466 |
<p>What equation would give me the answer to the question, "If i have a cup of water at a tempature of say boiling, how long would that cup of water take to cool off compared to say half that size of a cup of water." So the volume is in half. Its a general question I am just looking for where to start.</p> | 5,467 |
<p>I've read the definition of the electromagnetic field tensor to be
\begin{equation}F^{\mu\nu}\equiv\begin{pmatrix}0&E_x&E_y&E_z\\-E_x&0&B_z&-B_y\\-E_y&-B_z&0&B_x\\-E_z&B_y&-B_x&0\end{pmatrix}\hspace{0.5in}(\dagger)\end{equation}
in <em>Introduction to Electrodynamics</... | 5,468 |
<p>The expression $\int | \Psi\left(x\right)|^2dx$ gives the probability of finding a particle at a given position. </p>
<p>If wave function gives the probabilities of positions, why do we calculate "expectation value of position"?</p>
<p>I don't understand the conceptual difference, we already have a wave function o... | 5,469 |
<p>I've understood that the Cosmic Background Radiation(CBR) is an electromagnetic wave that originated from the big bang. However, we now live on a planet which that is also originating from the big bang.</p>
<p>Why does that Cosmic Background Radiation reaches us now? Why does CBR reaches us now, and not a couple of... | 5,470 |
<p>It's well known that the planets don't orbit the sun in perfect circles and the characteristics of the elliptical orbits which serve as better approximations to their motion have been calculated fairly accurately.</p>
<p>How accurately do elliptical orbits model their actual paths?</p> | 5,471 |
<p>What is meant with the fact that Super Yang-Mills flows to a conformal field theory in the infrared? Also, is this a general fact or does this depend on the fact of considering a certain class of theories (such as $N=4$, $d=3$ for example)?</p>
<p>I have seen this statement numerous times in various articles such a... | 5,472 |
<p>How would I calculate the uncertainty for the average of this set?</p>
<p>$32.5 \pm 0.1$</p>
<p>$32.0 \pm 0.1$</p>
<p>$32.3 \pm 0.1$</p> | 5,473 |
<p>Is there a real difference between <a href="http://en.wikipedia.org/wiki/Eternal_inflation" rel="nofollow">eternal inflation</a> and "chaotic inflation" theories? </p> | 5,474 |
<p>I'm trying to come up with an expression for the partition function of a system of spin-1/2 ideal gas particles on a line of length $L$. The total number of particles $N$ is fixed, with $N = N_\uparrow + N_\downarrow$. Here, $N_\uparrow$ is the number of spin-up particles and $N_\downarrow$ is the number of spin-dow... | 5,475 |
<p>According to the Newtons gravity we can write,
$$\vec F = \frac{\hat r_{12} G m_1 m_2 }{r_{12}^2}$$ and we are well known that this law satisfies the planetary motions. What changes will we see if we rewrite the law in this way,
$$\vec F = \frac{\hat r_{12} G m_1 m_2 }{r_{12}^{2+p}}$$ where p is a positive number. I... | 5,476 |
<p>According to Einstein's theory of relativity, the more speed something has the slower that time passes for it; and presumably when traveling at the speed of light, time stops entirely. So this means that when a photon is created, the rest of existence virtually pauses until the photon ceases to exist, and then the r... | 195 |
<p>We see variational principles coming into play in different places such as Classical Mechanics (Hamilton's principle which gives rise to the Euler-Lagrange equations), Optics (in the form of Fermat's principle) and even General Relativity (we get Einstein's equation from the Einstein-Hilbert action). However, how do... | 5,477 |
<p>A bucket is filled with water and a handful of sand. The water is then spun. Why and what forces are in play which cause the sand particles to congregate in the centre of the bucket?</p> | 196 |
<p>When walking, if I apply a force of 2N on the earth, the earth applies a force of 2N back on my feet due to Newtons 3rd Law of Motion. These 2 forces are equal in magnitude but opposite in direction, so they negate each other and add up to zero. So how can we move then if the net force adds up to zero? </p> | 197 |
<p><em>For topological insulators</em>
<strong>Is there any way to define <a href="http://www.google.com/search?as_q=order+parameter+topological+phase+transition" rel="nofollow">order parameter for topological phase transitions</a>?</strong></p> | 5,478 |
<p>In an arbitrary number of dimensions, one can naturally define two tensors, Kronecker delta and Levi-Civita epsilon tensor. However, why isn't it advantageous to define some totally symmetric tensor as well? Is there an intuitive reason for that or is it basically related to differential forms?</p> | 5,479 |
<p>I read that Wu's experiment illustrates that parity violation is possible for weak processes. In that experiment, when Co-60 undergoes beta decay, the emitted electrons come out opposite to the direction of nuclear spin. The mirror image process does not occur.</p>
<p>I also read that parity is conserved for EM and... | 5,480 |
<p>I'm interested in designing and building a Stirling engine which uses air that has been heated, which expands and then acts upon a piston producing power. </p>
<p>There is a fixed amount of air inside the sealed 2" cylinder, and a relatively stable heat supply. The piston compresses cool air and is powered by the e... | 5,481 |
<p><img src="http://i.stack.imgur.com/h8s8B.png" alt="enter image description here">
Consider a cell containing Rubidium and enlight it with a laser. Connect the system with an oscilloscope and give a triangular wave as input (so you can know when the Rubidium is resonant). This is the signal that you see downward. Yo... | 5,482 |
<p>Suppose I would like to have maximally physical image format. Which quantities should I store in the pixel? Obviously, it should be frequency spectrum, i.e. table with frequency vs. WHAT?</p>
<p>How to convert RGB values to any sort of physical quantities and vise versa?</p> | 5,483 |
<p>A charge is at rest in an inertial reference frame. </p>
<p>Consider this situation from the point of view of an observer who is accelerating relative to the charge. Would the observer observe electromagnetic waves generated by the charge?</p> | 5,484 |
<p>I found this explanation somewhere:
Since wavelength=c/freq so in a AC power line of 50 Hz, wavelength=(3*10^8)/50 = 6000 Km, so voltage phase reverses after 6000 Km in a ac Power line.</p>
<p>Now this would have been correct if it was a 50 Hz E.M. Transmission line, but does the same occur in metal wire with A.C. ... | 5,485 |
<p>Suppose we have a capacitor of capacitance $C$ and a cell of emf $E$, why is the maximum energy stored in a capacitor equal to $\tfrac{1}{2}CE^2$? I feel confused because, the potential difference against the capacitor will be less than the emf of the cell because of the potential drop across the resistor. What is t... | 5,486 |
<p>How to prove the identity
$$
\tilde {\sigma}_{\alpha}\sigma_{\beta}\tilde {\sigma}_{\gamma} = g_{\alpha \beta}\tilde {\sigma}_{\gamma} + g_{\alpha \gamma}\tilde {\sigma}_{\beta} - g_{\beta \gamma} \tilde {\sigma}_{\alpha} + i\varepsilon_{\alpha \beta \gamma \delta}\tilde {\sigma}^{\delta}, \qquad (1)
$$
where
$$
\si... | 5,487 |
<p>I am solving a Hamiltonian including a term $(x\cdot S)^2$.
The Hamiltonian is like this form:
\begin{equation}
H=L\cdot S+(x\cdot S)^2
\end{equation}
where $L$ is angular momentum operator and $S$ is spin operator. The eigenvalue for $L^2$ and $S^2$ are $l(l+1)$ and $s(s+1)$. </p>
<p>If the Hamiltonian only has th... | 5,488 |
<p>Whenever I have seen Venus described, its high surface temperature is attributed to an intense greenhouse effect. This seems to make sense, as its atmosphere is roughly 96% CO<sub>2</sub>. But on Earth, the greenhouse effect works because the atmosphere is (mostly) transparent to sunlight, but (somewhat) opaque to l... | 5,489 |
<p>I'm having a hard time understanding the deal with <a href="http://en.wikipedia.org/wiki/Self-adjoint_operator" rel="nofollow">self-adjoint differential opertors </a> used to solve a set of two coupled 2nd order PDEs.</p>
<p>The thing is, that the solution of the PDEs becomes numerically unstable and I've heared th... | 5,490 |
<p>So, I have a couple questions about transfer orbits.</p>
<p>As I understand it, an object's, say a satellite, orbit is basically tied to it velocity relative to the object, the planet, that it is orbiting.</p>
<p>The basic premise is that you have the satellite in a circular orbit of X radius, going speed v. Now, ... | 5,491 |
<p>Does the axis of Time point into a black hole or away from?</p>
<p>Can you give a reference paper?</p> | 5,492 |
<blockquote>
<p>The wheel of a car has a radius of 20 cm. It initially rotates at 120
rpm. In the next minute it makes 90 revolutions. What is the angular
acceleration?</p>
</blockquote>
<p>So the answer is solved by using one of the angular kinematic equations. More specifically delta theta. The problem I am ha... | 5,493 |
<p><em>I have encountered this claim while searching for sources answering " <a href="http://skeptics.stackexchange.com/questions/5310/can-we-see-the-curvature-of-earth-from-the-top-of-worlds-tallest-building">Can we see the curvature of earth from the top of world's tallest building?</a> ".</em></p>
<p>Wikipedia ... | 980 |
<p>I want to create a soap blaster using:</p>
<ol>
<li>a 1" hose with 8 bar compressed air</li>
<li>a non pressured container of soap and water mix</li>
<li><strong>without</strong> the use a pressurized tank</li>
</ol>
<p>I.e. something like this <a href="http://www.biltema.no/no/Verktoy/Trykkluft/Verktoy/Sandblasin... | 5,494 |
<p>Noether's Theorem is used to related the invariance under certain continuous transformations to conserved currents. A common example is that translations in spacetime correspond to the conservation of four-momentum.</p>
<p>In the case of angular momentum, the tensor (in special relativity) has 3 independent compone... | 252 |
<p>I'm not a current student at any school, but I am learning a new profession, and some of it is a basic understanding of elecrticity. I have some knowledge, but definitely not enough, and I have had to self teach most of what I know using old textbooks that I have found added to some military experience in ths subjec... | 5,495 |
<p>I learned that neutrinos have a much lower energy than electrons. Pair production of electrons occurs when the photon energy is above 2 times the energy of an electron. So I am wondering if pair production of neutrinos wouldn't be even more common and occur at much lower energy levels?</p> | 5,496 |
<p>Given d(slit separation)= $0.158\:\rm{mm}$, $\lambda _{red}= 665\:\rm{nm}$, $\lambda _{g/y}= 565nm$, L(distance from screen)= $2.24\:\rm{m}$</p>
<p>What is the distance between the third order red and green/yellow fringes? </p>
<p>I am using the equation $X _{3}= \frac{m \lambda L}{d}$ (just to find the distance t... | 5,497 |
<p>I know that in quantum mechanics there is no "time operator", so such a question is ill-posed. Anyway if the tunneling is instantaneous, this would imply an information transmission faster than $c$. On the other hand, how could someone define such a "time"?</p> | 5,498 |
<p>One of the weirdest things about quantum mechanics (QM) is the exponential growth of the dimensions of Hilbert space with increasing number of particles.
This was already discussed by Born and Schrodinger but here's a recent reference:</p>
<p><a href="http://arxiv.org/PS_cache/arxiv/pdf/0711/0711.4770v2.pdf" rel="n... | 5,499 |
<p>Does increasing the amount of electric charge on a conductor cause an increase in its <em>electric potential</em> to a point at which it becomes maximum; where it can hold no more extra charge?</p>
<p>Is it true? How?</p>
<p>I read it from a book while studying <em>capacitance</em>.</p>
<p>Does this idea sound <e... | 5,500 |
<p>One would say that $AdS_n$ satisfies the equations for the scalar curvature (R) and Ricci tensor ($R_{\mu \nu}$), $R = - \frac{n(n-1)}{L^2}$ and $R_{ab} = - \frac{n-1}{L^2}g_{ab}$. </p>
<ul>
<li>But do the signs in the above depend on the sign of the metric convention? </li>
</ul>
<hr>
<p>I am confused when I loo... | 5,501 |
<p>What's the conserved quantity corresponding to the generator of conformal transformations? </p> | 5,502 |
<p><strong>Problem</strong>: For a $P,V,T$ system with constant mass,entropy can be considered a function of $U,V$, i.e. $S=S(U,V)$. The goal is to derive the rest of the thermodynamic functions via Legendre transformations.</p>
<p><strong>Attempted answer</strong>:</p>
<p>I start with the 1st law of thermodynamics $... | 5,503 |
<p>On a <a href="https://en.wikipedia.org/wiki/Porkchop_plot" rel="nofollow">porkchop plot</a> for a given departure date (X axis), why are there two local energy minimums along the arrival date (Y-axis) for a transfer between Earth and Mars? The Hohmann transfer orbit seems to have one optimal solution, but the plot'... | 5,504 |
<p>I think I remember a talk where a professor said that <a href="http://en.wikipedia.org/wiki/4_Vesta" rel="nofollow">Vesta</a> is a particularly important asteroid because its gravity is strong enough to perturb other asteroids.</p>
<p>In spite of Vesta's size, this effect might be so strong that some smaller astero... | 5,505 |
<p>When trying to find the Fourier transform of the Coulomb potential</p>
<p>$$V(\mathbf{r})=-\frac{e^2}{r}$$</p>
<p>one is faced with the problem that the resulting integral is divergent. Usually, it is then argued to introduce a screening factor $e^{-\mu r}$ and take the limit $\lim_{\mu \to 0}$ at the end of the c... | 5,506 |
<p>I am studying a perturbed Toric Code model that is not analytically solvable.
On a torus the ground state degeneracy of the unperturbed model is 4.
Once we turn on the perturbation there is a change in the ground state degeneracy.
I would like to detect this change in ground state degeneracy numerically using exa... | 5,507 |
<p>I'm looking for the contactless methods to collect the information of the body construction especially skeletal structure to calculate in the computer model .
Are there physical methods to inspect internal side of the body other than X-ray and no any exposure of radiation ? For example, echo , MRI and so on . </p> | 5,508 |
<p>A photons energy is given by $E=h *f$ and momentum $p=E/c$ (spin?) but the photon has no (rest) mass! Therefore it is the ultimate probing tool for looking at any mass position and velocity because mass transfer is not involved only momentum.But to calculate/ measure the particles exact position by scattering a phot... | 5,509 |
<p>I'm quite stuck with this problem. </p>
<p>I know that I have an object in orbit. I know the eccentricity of that orbit, as well as the semi-major axis of the orbit. </p>
<p>Giving a <a href="http://en.wikipedia.org/wiki/True_anomaly" rel="nofollow">true anomaly</a>, how do I find the speed and altitude of that ob... | 5,510 |
<p>My question is regarding T-Duality between the 2 Type H string theories.</p>
<p>I know that the Type II String theories are T-dual to each other because T-Duality changes the sign of the Gamma Matrix so
$$\operatorname{T}:{{\cal P}}_{{\mathop{\rm GSO}\nolimits} }^ - \leftrightarrow {{\cal P}}_{{\mathop{\rm GSO}\no... | 5,511 |
<p>Is it correct to define Quantum Physics as the study of Physics in sub-atomic scale? Does Quantum Physics studies something else other than sub-atomic phenomena?</p>
<p>This may be a very stupid question but realize that I am <strong>!!!VERY NOOB!!!</strong> at Physics.</p> | 5,512 |
<p>In more detail:
If i have two soda cans, both are cooled to exactly 4 degrees celsius,
And i put one in a 25 degrees room, and the other next to an AC vent set to 16 degrees.
After three minutes, which one should be colder than the other and why?</p>
<p>Edit: To clarify - if I have a cold soda can, should I place i... | 5,513 |
<p>I was reading this page:</p>
<p><a href="http://www.guardian.co.uk/science/2011/oct/23/brian-cox-jeff-forshaw-answers" rel="nofollow">http://www.guardian.co.uk/science/2011/oct/23/brian-cox-jeff-forshaw-answers</a></p>
<p>and I found this sentence by Brian Cox:</p>
<blockquote>
<p>That seems to imply that every... | 5,514 |
<p>In <a href="http://arxiv.org/abs/1004.0726" rel="nofollow">this paper</a> on co-orbital dynamics the authors discover, numerically, "Anti-Lagrangian" solutions to the restricted 3 body problem. These Anti-Lagrange $L_4$ and $L_5$ points are 120 degrees ahead and behind the planet (if I understand correctly).</p>
<... | 5,515 |
<p>Let's say I have a cylindrical piston containing saturated liquid ammonia that is fitted with an electrical heater and a paddle wheel for stirring at an initial pressure and an initial temperature. When the gas expands, some of it evaporates to form a two phase, liquid-vapor solution inside the system. By the way, t... | 5,516 |
<p>Srednicki writes the Lagrangian density of an interacting scalar field theory as
$$ \mathcal{L} = -\frac{1}{2} Z_\phi \partial^\mu \phi \partial_\mu \phi -\frac{1}{2} Z_m m^2 \phi^2 + \frac{1}{6} Z_g g \phi^3 + Y\phi $$</p>
<p>He claims that $Y=O(g)$ and $Z_i=1+O(g^2)$. What is the basis of this claim?
Why do we ... | 5,517 |
<p>In general relativity, time-like geodesics are the trajectories of free-falling test particles, parametrized by proper time. Thus, they are easy to interpret in physical terms and are easy to measure (at least in principle).</p>
<p>Is there a similar interpretation/measurement for space-like geodesics? For example,... | 5,518 |
<p>Here's a homework problem I'm working on. I am not asking for the answer, but any guidance or comments on the approach are appreciated.</p>
<blockquote>
<p>Given that a measurement of $L^2$ for a free particle has resulted in the value $6\hbar^2$, what are the possible results for a measurement of $L_x$?</p>
</bl... | 5,519 |
<p>now, I have read a lot of explanations on that but still can't really understand why it would happen so if you can give some examples for a such a thing happening. I mean lets say gravity attracts the air and due to air viscosity all of the air gets carried with the Earth but why will the speed be same ? </p> | 162 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/2178/how-efficient-is-a-desktop-computer">How efficient is a desktop computer?</a> </p>
</blockquote>
<p>I believe the energy conversion efficiency of a modern CPU is extremely low, because it dissipates... | 198 |
<p>This diagram from <a href="http://en.wikipedia.org/wiki/Lagrangian_point">wikipedia</a> shows the gravitational potential energy of the sun-earth two body system, and demonstrates clearly the semi-stability of the L1, L2, and L3 lagrangian points. The blue arrows indicate lower potential energy, red higher - so any ... | 103 |
<p>I am taking a short introduction course on lasers. I never knew that the frequency of a laser is so high for a given wavelength (e.g. 780nm). I am wondering how people can measure the frequency of the laser. Do they downconvert the frequency of the light so that we could measure it with scope?</p> | 5,520 |
<p>A good buddy of mine and I have had a friendly debate about the origins of the current state of our universe (namely; Earth and life on Earth) and have fundamentally disagreed in our stances with respect to probabability, infinity in time and space and possible/probable event outcomes. He maintains the position that... | 5,521 |
<p>So I came across a question while studying laws of motion. Roughly, this is how it goes:
There are two astronauts in a space shuttle, who together have mass 200 kg. If by doing exercise, they manage to lose 80 kg, what will be the percentage increase in speed of the shuttle. The question is pretty straight forward, ... | 5,522 |
<p>Intuitively, if energy can be stored in rotational motion, it has to obey $E=mc^2$.
Does rotation of typical stellar-sized objects - BHs, pulsars, binaries - have measurable effect on their overall gravity? </p>
<p>(I'm not talking about nearby effects, like frame dragging described by Kerr metric, the effect on me... | 5,523 |
<p>suppose that, there is a plano convex lens and its thickness is 5.00cm. If you watch it straight from the convex side, it seems that its of 4.4 cm. What is the refractive index of this lens?</p> | 5,524 |
<p>We have studied so far that electric field inside a conductor if no charge is placed inside is zero. But we know that every conductor has only a limited number of electrons. What happens when ALL the electrons have aligned to cancel the field inside conductor under application of external field and then we increase... | 474 |
<p>Including air resistance, what is the escape velocity from the surface of the earth for a free-flying trajectile?</p> | 5,525 |
<p>I'm taking an optics lab in which I'm required to construct an interferometer, and measure the wavelength of a laser, and the coherence length of the light emitted from a candle fire.</p>
<p>Now, I've been hinted by my instructor that when working with mirrors (which are present in an interferometer), it is best to... | 5,526 |
<p>How do I go about finding the pressure exerted on a rectangular surface in a free flowing air stream?</p>
<p>I wouldn't imagine that this is directly related to the airspeed / surface area, but have no idea where to start. Is there even an equation, or does one need to do some kind of FEA?</p>
<p>For instance a 1.... | 5,527 |
<p>According to the first law of thermodynamics, sourced from wikipedia
"In any process in an isolated system, the total energy remains the same."</p>
<p>So when lasers are used for cooling in traps, similar to the description here: <a href="http://optics.colorado.edu/~kelvin/classes/opticslab/LaserCooling3.doc.pdf">h... | 608 |
<p>I have a question with regard to probabilistic quantum cloning - see for example <a href="http://prl.aps.org/abstract/PRL/v80/i22/p4999_1">http://prl.aps.org/abstract/PRL/v80/i22/p4999_1</a>.</p>
<p>It does seems like I can use the proof for no-cloning theorem to disproof the existence of equation (7) in the paper ... | 5,528 |
<p>Within my master's thesis, I try to model a machine elements and have to model the exact slipping and exact sticking between the bodies. So I noticed that such problems can be formulated as a LCP. </p>
<p>However I have difficulties at finding any literature where the usage is described well with examples..</p>
<p... | 5,529 |
<p>I have been reviewing the basics of mechanics in preparation of studying Spivak's text book on mechanics (I am from a more mathematical background and I am taking an advanced analytical mechanics course next quarter which is using this text). I recently came across a problem in a text different from the one that I ... | 5,530 |
<p>I have seen a few Dalitz plots so far and tried to understand how they are useful.
So one of the advantages of these plot is that the non-uniformity in the plots can tell something about the intermediate states that we cannot detect. My question is how do you extract the mass of these resonant particles from such pl... | 5,531 |
<p>Since a week or so a constant high pitch sound (~4khz) emanates from my active monitor speakers. After eliminating any ground or power source issues I noticed, that the sound rises in volume whenever I open my window - which is exactly between my speakers and an array of cellular antennas on the opposite building. I... | 5,532 |
<p>There are a lot papers explaining why Laughlin's wavefunction are energetically favorable, but seldom explain why a lower energy state could explain the plateau at $\nu=1/3$. I met at several places claims like: a lower energy state at $\nu=1/3$ will pin the electron density at $\nu=1/3$. But why is that? And what a... | 5,533 |
<p>At lower altitude an aeroplane usually has more lift. However an aeroplane flying at low altitudes (with gear/flaps up) at low velocity burns the same amount of fuel it would flying much faster at a higher altitude. Why?</p> | 5,534 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/18527/does-the-pauli-exclusion-principle-instantaneously-affect-distant-electrons">Does the Pauli exclusion principle instantaneously affect distant electrons?</a> </p>
</blockquote>
<p>If this rule work... | 199 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/18950/how-to-debunk-the-electric-universe">How to debunk ‘The Electric Universe’?</a> </p>
</blockquote>
<p>I am just wondering why there exists such a strong feeling within the physics community against... | 200 |
<p>Although the electromagnetic wave is made op of both electric and magnetic fields the electric field contributes much in vision and is thus, called the light vector. But, why is it that the electric field has a major role? </p> | 5,535 |
<p>The bar with length l, density r, diametr d, Young's modulus E, Poisson's ratio mu, is spinning around the cross-section, what is the change in the width of this bar?</p> | 5,536 |
<p>I watched this <a href="http://www.youtube.com/watch?v=_hmXrHvmwOM" rel="nofollow">video</a> featuring Michio Kaku explaining parallel universes. In the last two minutes he said that experiments in the LHC could reveal that there might be parallel universes and then he stops. What experiment was he talking about? An... | 5,537 |
<p>In one derivation of the corrected period of a pendulum, we started off like so: </p>
<p>The mass has a height $y$ given by $l(1-\cos \theta )$. $E = K + E \rightarrow \frac{1}{2}ml^2 \dot{\theta}^2 + mgl(1-\cos \theta)$</p>
<p>The next step introduces $\theta _0$, and I've got no idea where this came from. </p>
... | 5,538 |
<p>The game <a href="http://gamelab.mit.edu/games/a-slower-speed-of-light/">"A slower speed of light"</a> from MIT claims to simulate effects of special relativity:</p>
<blockquote>
<p>Visual effects of special relativity gradually become apparent to the
player, increasing the challenge of gameplay. These effects,... | 5,539 |
<p>I have read that plasma is a state of matter that resembles gas but it consists of ions and electrons coexisting. So my question is : If plasma is just ionized gas, will ideal gas law apply for it ?</p> | 5,540 |
<p><img src="http://i.stack.imgur.com/GkwGl.jpg" alt="enter image description here"></p>
<p>How eq(4.4) is a solution of eq(4.3) </p> | 5,541 |
<p><a href="http://en.wikipedia.org/wiki/Stern%E2%80%93Gerlach_experiment" rel="nofollow">The Stern Gerlach experiment</a> was meant to prove the orbital quantization of electrons where there should be +ml,0,-ml states. So for l=2, there should be 5 beams.</p>
<p>But they saw 2 beams, which was shown to be due to the ... | 5,542 |
<p>For a static electric field $E$ the conservation of energy gives rise to $$\oint E\cdot ds =0$$ Is there an analogous mathematical expression the conservation of momentum gives rise to?</p> | 5,543 |
<p>....is an oblate spheroid because centrifugal force stretches the tropical regions to a point farther from the center than they would be if the planet did not rotate. So we all learned in childhood, and it seems perfectly obvious. However...</p>
<p>I am at $45^\circ$ north latitude. Does that mean</p>
<ul>
<li>... | 5,544 |
<p>The argument for <a href="http://en.wikipedia.org/wiki/Eternal_inflation" rel="nofollow">eternal inflation</a> is we have some patch of metastable vacuum with positive cosmological constant, and so it expands exponentially a la de Sitter. Most of the patch decays to something which expands more slowly, but only a ti... | 5,545 |
<p>Schrodinger believed that the phisical interpretation of the wavefunction $\Psi$ was the vibration amplitude and $ |\Psi|^2 $ was the electric charge density. While no-one disagrees with his interpretation of $\Psi$, many physicists believed Schrodinger was wrong about about $|\Psi|^2$ and argued that $|\Psi|^2$ is... | 5,546 |
<p>I have tough problem I am not sure how to solve:</p>
<p>For this question, we are confined to a plane. Consider a gravitational field that is proportional to $\frac{1}{r^3}$ instead of $\frac{1}{r^2}$, and consider its potential which is then proportional to $\frac{1}{r^2}$. Suppose that I put $n$ identical point... | 5,547 |
<p>I was wondering, why in Newtonian physics <a href="http://en.wikipedia.org/wiki/Torque" rel="nofollow">torque</a> is called "torque" while in static mechanics they call it "moment"? </p>
<p>I prefer by far the term "torque", for not only it sounds strong, but also instead of moment, the correct synonym of torque is... | 5,548 |
<p>There is a recent paper on arxiv receiving lot of acclaim <a href="http://arxiv.org/abs/1105.4714">http://arxiv.org/abs/1105.4714</a></p>
<p>The authors experimentally show that moving a mirror of a cavity at high speeds produces light from high vacuum. The usual doubts about the experimental techniques seem to be ... | 5,549 |
<p>Landau writes "It is found, however, that a frame of reference can always be chosen in
which space is homogeneous and isotropic and time is homogeneous."</p>
<p>Does he mean that we can prove the existence of an inertial frame or does he want to say that it is assumed by doing enough number of experiments?</p>
<p... | 5,550 |
<p>Supposing there is an iron nail that is left to rust, if we compare the time it takes to rust with that of a magnetized iron nail, will there be any difference in the time of corrosion (assuming other environmental factors are constant)?</p> | 5,551 |
<p>Well I have a couple of questions regarding Black holes so here they are,</p>
<p>1.Shouldn't they be called black spheres?(holes are in 2D right?)</p>
<p>2.What will happen if black holes collide?(If they can)</p>
<p>3.Will they have the "information" of what they have eaten?</p>
<p>4.What's a white hole?
(i'm o... | 5,552 |
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