question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>I would like to know why dry frictional force does not depend on speed(assuming that the heat generated by friction is small so it does not alter the coefficient of friction). </p>
<p>Let me explain how I think about dry friction. When I slide one object on another than their small irregularities on surfaces are ba... | 2,345 |
<p>Consider a particle in a potential well. Let’s assume it’s a simple harmonic oscillator potential and the particle is in its ground state with energy E<sub>0</sub> = (1/2) ℏω<sub>0</sub>. We <strong>measure</strong> its position (measurement-1) with a high degree of accuracy which localises the particle,... | 2,346 |
<p>How the notion of <em>weak measurement</em> resolves <a href="http://en.wikipedia.org/wiki/Hardy%27s_paradox" rel="nofollow">Hardy's paradox</a>?</p> | 2,347 |
<p>In general, the Hamiltonian $H$ has non-zero vacuum expectation value (VEV):
$$ H \left.| \Omega \right> = E_0 \left.|\Omega \right>, $$ where $\left.|\Omega\right>$ is the vacuum state. The zero-point energy of the quantum oscillator is a good example to have non-vanishing VEV.</p>
<p>The problem strikes ... | 2,348 |
<p>I'm asked to calculate how much POWER a 1210kg car needs to drive with a 85 km/s speed up a 655 meter long slope of 4.5°. I can find how much energy and work is required to do this, but isn't POWER=WORK over TIME? I don't have any time in my problem.</p>
<p>So I ask: If I have a 1000kg car and I drive 500 meters...... | 2,349 |
<p>The <a href="http://en.wikipedia.org/wiki/Feynman_checkerboard" rel="nofollow">Feynman Checkerboard Wikipedia article</a> states: "There has been no consensus on an optimal extension of the Chessboard model to a fully four-dimensional space-time."</p>
<p>Why is it hard to extend it to more than 1+1 dimensions?</p> | 2,350 |
<p>What is the meaning, mathematical or physical, of the anti-commutator term?
$\langle ( \Delta A )^{2} \rangle \langle ( \Delta B )^{2} \rangle \geq \dfrac{1}{4} \vert \langle [ A,B ] \rangle \vert^{2} + \dfrac{1}{4} \vert \langle \{ \Delta A, \Delta B \} \rangle \vert^{2}$,
where $\Delta A, \Delta B, A$ and $ B$ are... | 2,351 |
<p>In my blog post <em><a href="http://thespectrumofriemannium.wordpress.com/2012/11/07/log050-why-riemannium/" rel="nofollow">Why riemannium?</a></em> , I introduced the following idea. The <a href="http://en.wikipedia.org/wiki/Particle_in_a_box" rel="nofollow">infinite potential well</a> in quantum mechanics, <a href... | 2,352 |
<p>What are some of the most elegant/complex/sophisticated physics experiments one could perform in his garage, if he has enough spare time and technical/theoretical know-how, but a relatively limited budget? Say, a retired emeritus physics professor?</p>
<p>These could be either novel or reproductions of known experi... | 2,353 |
<p>I have observed that the power lines buzz louder when there is less moisture in the air.</p>
<p>Why is this?</p>
<p>If it will help the lines are located on the foot hills of a nearby mountain.</p> | 2,354 |
<p>I will probably be laughed out of town for saying this, but why can't the Energy Conservation Law be broken?</p>
<p>Everybody thought electricity to motion was impossible until Faraday made his motor, nobody believed Tesla would make a <a href="http://en.wikipedia.org/wiki/Brushless_DC_electric_motor" rel="nofollow... | 2,355 |
<p>Suppose 2 capacitors are connected in series, the plates connected to the battery terminals receive charges $+q$ and $-q$, and the isolated plates in the combination receive equal and opposite charges through induction. Now my question is, why is that the induced opposite charge on the plates isolated (i.e. not conn... | 2,356 |
<p>I have a Sunbeam home espresso machine with a steam wand. The steam roars out straight from the end of the wand. When it's first placed in the cold milk it really screams! Once the milk has a bit of a whirlpool action going it's much quieter, so I guess that the noise is because of fast-moving steam hitting stationa... | 2,357 |
<p>I understand that when cooling water with <a href="http://en.wikipedia.org/wiki/Liquid_nitrogen" rel="nofollow">LN2</a> directly (through pipes for example), that it can be too effective, freezing the water (and blocking the pipe). </p>
<p>From what I read, regulation of the heat transfer is considered complicated ... | 2,358 |
<p>I don't understand whether something physical, like velocity for example, has a single correct classification as either a contravariant vector or a covariant vector. I have seen texts indicate that displacements are contravariant vectors and gradients of scalar fields are covariant vectors, but in <i>A Student's Gui... | 2,359 |
<p>I know that Quantum Hall Effect and Fractional Quantum Hall Effect origin from Landau Level quantization.</p>
<p>In magnetic field, the energy of in-plane(plane perpendicular to magnetic field) degree of motion is quantized, which is $E=(n+1/2)\hbar\omega$, $n$ is integer.</p>
<p>In experiment, both QHE and FQHE a... | 2,360 |
<p>I am an engineering student who is interested in orbital mechanics. I am doing some self study before taking some orbital mechanics courses next year. I was learning about various orbit types (elliptical, parabolic, hyperbolic, etc.) and the effects of burning in various directions. I have found a lot of good inf... | 2,361 |
<p>Perfectly localized states are not normalized so do not belong to the Fock space (they belong to the rigged version). Suppose we approximate localized states with gaussians, what is the mathematical expression for two "approximately" localized particles at points $x_1$ and $x_2$ that takes into account correlations ... | 2,362 |
<p><a href="http://en.wikipedia.org/wiki/Kirchhoff%27s_law_of_thermal_radiation" rel="nofollow">Kirchhoff's law of thermal radiation</a> states that for thermal equilibrium for a particular surface the monochromatic emissivity $\epsilon_{\lambda}$ equals the monochromatic absorptivity $\alpha_{\lambda}$:
$$\alpha_{\lam... | 2,363 |
<p>I've finally managed to get a grasp on the <a href="http://en.wikipedia.org/wiki/Bell_test_experiments" rel="nofollow">Bell test experiments</a> and all that they imply about our reality. Now I'm curious about the mathematical derivation which allowed Schrodinger to predict the existence of entangled entities.</p>
... | 2,364 |
<p>For the past years I am thinking about relating concepts from physics to concepts from economics. Especially since the financial crisis made obvious the instability of the financial system I ask myself whether this could be explained by physics, e.g. by lack of inertia and dissipation during transactions, conservati... | 2,365 |
<p>If the strong nuclear force were just 2% stronger, the neutron would be a stable particle instead of having a half life of about 13 minutes. What difference would that have made to Big Bang nucleosynthesis, to the growth of structure, to the formation of stars, nucleosynthesis in stars?</p> | 2,366 |
<p>Extending the Gaussian model by introducing a second field and coupling it to the other field, I consider the Hamiltonian</p>
<p>$$\beta H = \frac{1}{(2\pi)^d} \int_0^\Lambda d^d q \frac{t + Kq^2}{2} |m(q)|^2 +
\frac{L}{2} q^4 |\phi|^2 + v q^2 m(q) \phi^*(q)$$</p>
<p>Doing a Renormalization Group treatment, I in... | 2,367 |
<p>According to L&L, if we fix the initial position of a particle at a given time and consider the on-shell action as a function of the final coordinates and time, $S(q_1, \ldots, q_n, t)$, then...</p>
<p>$$E = -\frac{\partial S}{\partial t}$$</p>
<p>$$p_i = \frac{\partial S}{\partial q_i}$$</p>
<p>Is there a st... | 2,368 |
<p>Today I heard an argument to prove that the Earth-Centered Earth-Fixed (<a href="http://en.wikipedia.org/wiki/ECEF" rel="nofollow">ECEF</a>) reference frame is non-inertial. It seriously doesn't make any sense to me but I also heard that same argument was made by Einstein, so I am asking it here. Please explain how ... | 2,369 |
<p><a href="http://en.wikipedia.org/wiki/Critical_mass">Wikipedia</a> gives the following definition for critical mass.</p>
<blockquote>
<p>A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction.</p>
</blockquote>
<p>No mention is made of a neutron moderator in this... | 323 |
<p>In the figure, blocks A and B have weights of 45 N and 23 N, respectively. (a) Determine the minimum weight of block C to keep A from sliding if μs between A and the table is 0.21. (b) Block C suddenly is lifted off A. What is the acceleration of block A if $\mu_k$ between A and the table is 0.14?</p>
<p><img src="... | 2,370 |
<p>Suppose I have a flow of hot air around a cold and unevenly shaped object with holes and tunnels (think about it as a bed packed with some objects). I would like to know the Reynolds number of this flow and its convective heat transfer coefficient. The definition of the Reynolds number contains a "characteristic len... | 2,371 |
<p>The Riemann curvature of a unit sphere is shown in many textbooks to be sine-squared theta where theta is the azimuthal angle of spherical co-ordinates. But what is the significance of the angle and how would a value be assigned to it?</p> | 2,372 |
<p>Given a quantum state function, we can Fourier expand it in terms of stationary states of the Hamiltonian. So if we want to build that same quantum state approximately all we need to do is to superpose stationary states with proper amplitudes. Assuming that we can prepare such stationary states individually, how is ... | 2,373 |
<p>A theory of quantum gravity is said to be needed when quantum and gravitational effects are strong at the same time i.e. at black hole singularities and at the big bang. This also makes it difficult to test quantum gravity.</p>
<p>But what about testing <a href="http://en.wikipedia.org/wiki/Macroscopic_quantum_phen... | 2,374 |
<p>New physics is expected at high energies and cosmic rays have high energies, so have there been or are there any plans to put <a href="http://en.wikipedia.org/wiki/Particle_detector" rel="nofollow">particle detectors</a> in space to study cosmic rays for new physics ?</p> | 2,375 |
<p>Since <a href="http://en.wikipedia.org/wiki/Anyon#Non-abelian_anyons" rel="nofollow">non-abelian anyons</a> have become quite fashionable from the point of view of theory. I would like to know, whether there has actually been experimental confirmation of such objects.
If you could cite original literature, that woul... | 2,376 |
<p>I made some calculations about flow from the bottle, but problems occured when the experimental data came back. Need to refine calculations, but problems occur when trying to link the angle to the flow, because volume changes constantly, and volume that has left in the bottle is governed by the force sensor. And the... | 2,377 |
<p>I have seen Gauss Law being used for a uniformly charged hollow sphere rotating with $\omega$. How is that valid to use Gauss law since it is an electrostatic law and if it is valid, why do we get a net constant electric field outside the sphere inspite of the accelerating charges - does the net time dependence canc... | 2,378 |
<p>Cosmology (and astrophysics) talk about the "initial singularity" (IS, became the big bang) and "black hole singularities" (BS, inside black holes), and these appear to be quite different: The IS is described as having <strong>zero volume and infinitely high temperature and density</strong>, whereas the BS is likewi... | 2,379 |
<p>The reduced mass in the two body problem is $\mu= \cfrac{m_1 m_2}{m_1 + m_2}$. Is there any analog to this with interacting charged particles (or at least that is of use somewhere in physics)? I have not seen anything like this anywhere, but was curious if someone else has. I would imagine that this is not possible... | 2,380 |
<p>I was thinking about a situation were I have a long cylindrical jar with some viscous liquid in it. I also have a spherical ball with me. I drop the ball into the liquid inside the jar with some initial velocity. Just after that(before the ball acquires terminal velocity) I drop the system(the jar with the liquid an... | 2,381 |
<p>I'm trying to figure out which object would have the largest time of flight when launched from a slingshot. To do this, I need the initial velocity. How can I calculate this if I know the mass and diameter of the object? The slingshot always has the same force. I've seen a number of formulas, but none of them take i... | 2,382 |
<p>Organic semiconductors differ from inorganic semiconductors. In organic semiconductors the molecules are held together by weak van der Waals interactions and in inorganic semiconductors by covalent bonds. So the bonds are different. How do you express the main difference between the twos? Is it the electronic struct... | 2,383 |
<p>I have a thought-experiment sort of question and I don't know where to start. Suppose you have an entangled pair, e1 and e2, and you split them. Then BEFORE reading them, you spin control e1 to +, then e2 would be -, correct?</p>
<p>Can you then, AFTER, reapply spin control to e1 and make it -. Would e2 then flip b... | 2,384 |
<p>Given: </p>
<ul>
<li>The pulley is moving towards the right.</li>
<li>All blocks have different masses. (The pulley and the strings are massless.)</li>
</ul>
<p><img src="http://i.stack.imgur.com/unSZF.png" alt="Pulley">
What I don't understand:</p>
<ul>
<li>Is the tension the same for both A and B?</li>
<li>If t... | 2,385 |
<p>Basically, a simple capacitor will consist of 2 plates and a dielectric material between them, what if i took 2 plates, charged one with a +ve charge and the other with equal -ve charge, then i put them together with a dielectric material between them , then i connect them with a wire so it can discharge , can i con... | 2,386 |
<p>Before I start, I'm aware that this question may be better suited on the Chemistry or Biology site, but it's my belief that physicists are more likely to have a clear understanding on what certain terms mean, so by all means move the question if you feel like it will get a better response elsewhere.</p>
<p>Okay.</p... | 2,387 |
<p>and that is the internal motion relative to the center of mass?
could give me some examples?
desire to relate since I need to find out what is the kinetic energy in the center-of-mass of two particles, one moving and one stationary.
Note: they collide</p> | 2,388 |
<p>Assume you charge a (parallel plate) capacitor. This establishes an electric field (the $\mathbf E$ vector points from one plate to the other) and a circular magnetic field (the $\mathbf B$ vector points tangential to circles centered at the capacitors main axis) while the Poynting vector points inwards.</p>
<p>Wou... | 2,389 |
<p>I assume that the refrigerator's temperature of 4 degrees has something to do with the fact that water is densest at that temperature. Does that inhibit microbe growth? But what about the freezer, what is special about -18 degrees? Is it a trade off of some type?</p> | 2,390 |
<p>There is <a href="http://en.wikipedia.org/wiki/Electromagnetic_induction" rel="nofollow">a famous law</a> which says that a potential difference is produced across a conductor when it is exposed to a varying MF. But, how do you measure it to prove? It is quite practical. </p>
<p>Particularly, I had once a problem d... | 2,391 |
<p>Consider a stationary solution with stress-energy $T_{ab}$ in the context of linearized gravity. Choose a global inertial coordinate system for the flat metric $\eta_{ab}$ so that the "time direction" $(\frac{\partial }{\partial t})^{a}$ of this coordinate system agrees with the time-like killing vector field $\xi^{... | 2,392 |
<p>I'm trying to figure out an example from a textbook (Demtröder -- Experimentalphysik 2, pg. 198) where the energy transport caused by a current is depicted:</p>
<p>Assume you have a wire (with some resistance $R$) and a current $I$ flowing through the wire. The wire will emit energy in form of heat (with $\dot W = ... | 2,393 |
<p>It's not possible for an electron to emit or absorb a photon without the presence of a third particle such as an atomic nucleus; without the third particle, it's impossible for such a process to conserve energy and momentum.</p>
<p>However, if tachyons exist and couple to matter, then a material particle can emit ... | 2,394 |
<p>I found multiple questions where it is stated that dark energy increases as the universe expands. Assuming a big crunch scenario, will this dark energy "go away" again as the size of the universe decreases again, or will there be more energy (=mass) at the Big Crunch than at the Big Bang?</p> | 2,395 |
<p>You can have two electrons that experience each other's force by the exchange of photons (i.e. the electromagnetic force). Yet if you compress them really strongly, the electromagnetic interaction will no longer be the main force pushing them apart to balance the force that pushes them towards each other. Instead, y... | 2,396 |
<p>Assume stably stratified fluid but not in equilibrium, e.g. with non-constant temperature gradient for example. Can convection cells be present? Typical example of convection cells is Rayleigh–Bénard convection. But this is example of unstably stratified fluid. In stably stratified fluid which is not in equilibrium ... | 2,397 |
<p>...to heat a piece of steel so its glowing yellow (1100 C)? Assuming you had a cloudless day at a latitude of, say, San Francisco...</p>
<p>Basically I'm wondering if it is possible/feasible to be able to do basic metal working without a traditional forge, just using the power of the sun to heat the metal. So the d... | 2,398 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/44629/elastic-collision-and-momentum">Elastic Collision And Momentum</a> </p>
</blockquote>
<p>I've already asked this question, <a href="http://physics.stackexchange.com/questions/44629/elastic-collisio... | 44 |
<p>I think I do not understand well the concept of Deborah number.</p>
<p>It is presented in the sources available to me as the ratio between the relaxation time of a fluid and a characteristic time scale of the flow. In other sources the denominator of the ratio is occupied by the "observation time scale".</p>
<p>Fi... | 2,399 |
<p>So I was wondering if Electromagnetic wave has the same property of interference as normal waves. I understand that both the electric and magnetic parts of the wave would have to be in the same position at the same time. To negotiate the fact that only one part of the wave would match up at one time due to the fact ... | 2,400 |
<p>I have been performing an experiment at school in which I test the force on an iron surface from the magnetic field of an electromagnet. The electromagnet has a rectangular iron core. The theory predicts that the force increases linear with the surface area of the iron plate. This is because the volume between the p... | 2,401 |
<p>If a mass of one kilogram is traveling at one meter per second at 90 degrees, how much energy is required to get it to travel going 180 Degrees?</p> | 2,402 |
<p>I'm trying to think about special relativity without "spoiling" it by looking up the answer; I hope someone can offer some insight - or at least tell me I'm wrong. </p>
<p>Suppose I have an ordinary clock in front of me and I push it back with my hands. The force applied to the clock causes it to retreat away fro... | 2,403 |
<p>It's said that if a space elevator were made then it would be much more efficient to put objects in orbit. I've always wondered about the durability of a space elevator though. I don't mean the material strength but rather what affect using the elevator has on the elevator.</p>
<p>To put some massive object in or... | 2,404 |
<p>Say you have energy eigenstates</p>
<p>\begin{align}
\begin{split}
|+\rangle=
\frac{1}{\sqrt{2}}|1{\rangle}+\frac{1}{\sqrt{2}}|2 \rangle
\end{split}
\end{align}</p>
<p>\begin{align}
\begin{split}
|-\rangle=
\frac{1}{\sqrt{2}}|1{\rangle}-\frac{1}{\sqrt{2}}|2 \rangle
\end{split}
\end{align}</p>
<p>with </p>
<p>\... | 2,405 |
<p>What would be the proof for $\langle q| p \rangle = e^{ipq}$?</p>
<p>Is it derived from canonical commutation relation?</p>
<p>($|q \rangle $ represents the position eigenstate, while $|p \rangle$ represents the momentum eigenstate.)</p> | 2,406 |
<p>The answers to <a href="http://physics.stackexchange.com/q/134473/58796">Where does the extra kinetic energy come from in a gravitational slingshot?</a> state that in a gravitational slingshot the object being accelerated "steal" speed from the planet (or moon).
Does that mean that an excessive number of g-slingshot... | 2,407 |
<p>Imagine you have a simple pendulum hanging on the ceiling of a train which has a period called T. How will the period be in the following cases:</p>
<ol>
<li>When the train is in circular motion in a curve of radius R with constant speed (I think it would be lower than T (the initial period), that's my intuition).<... | 2,408 |
<p>I don't understand why this formula is relevant to the problem:</p>
<p><img src="http://i.stack.imgur.com/9t26Y.png" alt="enter image description here"></p>
<p>This was the relevant worked solution:</p>
<p><img src="http://i.stack.imgur.com/rnX8F.png" alt="enter image description here"></p>
<p><strong>My problem... | 2,409 |
<p>I was trying to solve this problem:</p>
<p>"A punctiform source of light is standing inside a lake, at a height h of the surface. f is the fraction of the total of energy emitted that escapes directly from the lake, ignoring the light being absorbed in the water. Given n, the refractive index of water, determine f.... | 2,410 |
<p>To preface, I am not a scientific mind, but a writer looking for some validity to a possible scene. That being said, please forgive me!</p>
<p>In my scene, huge masses of fire are raining from the sky and crashing into a salt-water ocean. </p>
<p>[Edit]: I would imagine the buring substance as some sort of 'napalm... | 2,411 |
<p>I want to check that I am getting the concept right here, and my question is: if the expectation value of a Hamiltonian is the same whether you use the time dependent version or not. I thought I had it right initially -- maybe I did -- but I wanted to make sure I didn't go off the rails somewhere. </p>
<p>We have a... | 2,412 |
<p>If a conductor carrying current is placed inside a magnetic field, we know that there is the Lorentz force pushing the wire. But what about the attraction force between the wire's field and the magnet/electromagnet's field? So, isn't there really two forces involved? Attraction due to two magnetic field, and Lorentz... | 2,413 |
<p>I would like some help with the explicit math steps to go from equation 2 to 3. These equations are presented in a paper that I am reading. I will show where these equations came from and my attempt further below. The paper reads:</p>
<blockquote>
<p>The volumetric isothermal flow rate of nitrogen, which behav... | 2,414 |
<p>Any object traveling at c is observed as traveling at c in all reference frames. When a photon travels through a vacuum at c, all reference frames observe it traveling at c.</p>
<p>When a photon passes through a medium, it's speed is less than c. The moment that it begins to slow down, there is a reference frame in... | 2,415 |
<p>I'm looking for an online coupled oscillation simulation. The best I have got so far is this ---</p>
<p><a href="https://phet.colorado.edu/sims/normal-modes/normal-modes_en.html" rel="nofollow">https://phet.colorado.edu/sims/normal-modes/normal-modes_en.html</a></p>
<p>But I'm looking for something which has more ... | 2,416 |
<p>Let's consider an extended version of the Standard Model (SM) with a new Yukawa operator of the form
$$ \sum_\ell g_\ell\bar{\ell}\ell \phi ,$$
where $\ell$ is any lepton of the SM and $\phi$ is a new real spin-0 particle, which is assumed to be a singlet of $SU(2)_L$. This new term breaks the $SU(2)_L$ symmetry, bu... | 2,417 |
<p>I'm trying to understand how infinite mass corrections are cancelled for a particle that is massless at tree level. In short the problem is that we have infinite diagrams, but we don't have a counterterm for them since they don't exist at tree level. As a simple example consider a theory with three charged Weyl ferm... | 2,418 |
<p>I've edited my original question into horrible monstrosity (I apologize to all who spent their time on it). Here is rephrased version which hopefully will be clear.</p>
<p>Lets have following model situation concerning Poynting's theorem.</p>
<blockquote>
<p><em>Only one standing charged particle in studied area... | 2,419 |
<p>In the flat spacetime, one can perform normal-ordering to set the energy of the vacuum state to zero. I read in some places that this procedure cannot be consistently performed in the curved spacetimes. I have not found any explanation of this fact in the literature.
Why is this a case? </p> | 2,420 |
<p>I was wondering what would happen to all the components on the surface of the Earth if the Earth suddenly stops rotating but does not stop revolving.</p> | 45 |
<p>I want to prove the following relation</p>
<blockquote>
<p>\begin{align}
\epsilon_{ijk}\epsilon^{pqk}
=
\delta_{i}^{p}\delta_{j}^{q}-\delta_{i}^{q}\delta_{j}^{p}
\end{align}</p>
</blockquote>
<p>I tried expanding the sum
\begin{align}
\epsilon_{ijk}\epsilon^{pqk}
&=&
\epsilon_{ij1}\epsilon^{pq1}
+
\epsil... | 2,421 |
<p>The gravitational binding energy of a sphere is: $U=\frac{3GM^2}{5r}$, the mass defect is $\Delta E=\Delta m c^2$. Putting: $M=\frac{4}{3}\rho\pi r^3$, we get:
$$U=\frac{16}{15}G\rho^2\pi^2 r^5$$. Now if we put: $U=\Delta E$, we get for $r$:
$$r=\frac{1}{2}\frac{\sqrt5c}{\sqrt{G\rho\pi}}$$ that means:
$$r\approx\fra... | 2,422 |
<p>I encountered a few times the expression of <a href="http://www.google.com/search?as_q=%22statistical+physics%22&as_epq=height+field" rel="nofollow">'height fields' in statistical physics</a>, without ever reading a proper definition. My textbooks don't seem to talk about that, and googling it hasn't been fruitf... | 2,423 |
<p>Suppose you have 1 kg of lead, can the whole thing be converted into energy so that no mass remains? Or does the conversion stop at the protons/neutrons?</p> | 46 |
<p>Is it possible to create a telescope with only one convex lens?</p>
<p>Specifically, is the image I drew below possible?<br>
(This was supposed to be rotated 90 degrees counterclockwise.)</p>
<p><img src="http://i.stack.imgur.com/KUkVl.jpg" alt="Picture of my hypothesis(?)"></p>
<p>In this picture, the object (s... | 2,424 |
<p>I learned in elementary school that you could get <code>green</code> by mixing <code>blue</code> with <code>yellow</code>. </p>
<p>However with LEDs, TFTs, etc. you always have RGB (red, green, blue) values?</p>
<p>Why is that? From what you learned in elementary <code>yellow</code> would be the 'natural' choice i... | 2,425 |
<p>In book <a href="http://rads.stackoverflow.com/amzn/click/0070206503" rel="nofollow">"Quantum Mechanics and Path Integral"</a>, 3-2 Diffraction through the slit:</p>
<p>Under the fig. 3-3, why did Feynman say that we cannot approach the problem by a single application of the free-particle law motion, since the part... | 2,426 |
<p>Consider the following peculiar Lagrangian with two degrees of freedom $q_1$ and $q_2$</p>
<p>$$ L = \dot q_1 q_2 + q_1\dot q_2 -\frac12(q_1^2 + q_2^2) $$</p>
<p>and the goal is to properly quantize it, following <a href="http://en.wikipedia.org/wiki/Dirac_bracket" rel="nofollow">Dirac's constrained quantization p... | 2,427 |
<p>I saw a great documentary last night about 'nothing'. It's about vacuums, and how if you have a total vacuum atoms will pop out of nowhere! Pretty crazy stuff. Atoms literally coming out of nowhere, then disappearing quickly.</p>
<p>It got me thinking, before the big bang if there was nothing, then presumably at... | 2,428 |
<p>I know that if I integrate probabilitlity $|\psi|^2$ over a whole volume $V$ I am supposed to get 1. This equation describes this.</p>
<p>$$\int \limits^{}_{V} \left|\psi \right|^2 \, \textrm{d} V = 1\\$$</p>
<p>How would we calculate a normalisation factor $\psi_0$ for two simple wave functions like:</p>
<p>$$
\... | 2,429 |
<p>To any nonmagnet, the whole sphere is a magnet. To another spherical magnet though, there is a rough area on the surface where it is strongly repelled. </p>
<p>Given a spherical magnet, <em>how should the poles be found</em>? </p>
<p>My crude attempts were as follows</p>
<ul>
<li>Grip one sphere in a forceps</li>... | 2,430 |
<p>I'm working with a megapixel camera and lens that needs to be focused for an OCR application. In order to measure the focus quality during the set-up, I've built a tool that gives the contrast value between two pixels. In very simply words, more the contrast is high more the focus is good...
Due to optical distortio... | 2,431 |
<p>I always wonder how vectors are used in real life.Vectors and decomposition of vectors,dot and cross products are taught in the early stage in every undergraduate physics course and in every university.My question is how and where are vectors used? <strong>Do physicists really use vectors in every day life? If so wh... | 2,432 |
<p>I found Sean Carroll's "A No Nonsense Introduction to General Relativity" (about page <a href="http://preposterousuniverse.com/grnotes/">here</a>. pdf <a href="http://preposterousuniverse.com/grnotes/grtinypdf.pdf">here</a>), a 24-page overview of the topic, very helpful for beginning study. It all got me over the... | 89 |
<p>Let's say I have:</p>
<p>1: one mole of extremely cold ideal gas<br>
2: unlimited amount of ideal gas at temperature 300 K<br>
3: one ideal heat engine</p>
<p>Can I generate for example 1 MWh of mechanical energy using those three things? </p>
<p>Alternative formulation: When temperature of the cold gas approach... | 2,433 |
<p>If I charge a capacitor ($220\mu{F}$) using a 6V battery, and then measure the time it takes to discharge 90% of the initial energy over a resistor (${100k}\Omega$), and then charge the same capacitor using a 12V battery and measure the time it takes to discharge 90% of its initial energy again (over the same resist... | 2,434 |
<p>I've come across black holes thermodynamics multiple times recently (both at this site and elsewhere) and some things started bugging me.</p>
<p>For one thing, first law bothers me a little. It is a reflection of the law of conservation of energy. This is fine when the space-time is stationary (as in Kerr solution)... | 2,435 |
<p>If the captured object do not have tangential velocity, it's just the free-fall time. But when it has, it may take longer time to fall in, right ?</p>
<p>The function should be </p>
<p>$\ddot{r} = -GM/r^2 + (v_0r_0/r)^2 / r = -GM/r^2 + v_0^2r_0^2 / r^3$ , </p>
<p>where v_0 is the initial tangential velocity . Af... | 2,436 |
<p>Some time ago I came across a problem which might be of interest to the physics.se, I think. The problem sounds like a homework problem, but I think it is not trivial (i am still thinking about it):</p>
<p>Consider a rail tank wagon filled with liquid, say water.<img src="http://i.stack.imgur.com/nunmv.jpg" alt="wa... | 800 |
<p>How can I derive the Euler-Lagrange equations valid in the field of special relativity? Specifically, consider a scalar field.</p> | 2,437 |
<p>I'm reading <em>Nano: The Essentials</em> by T. Pradeep and I came upon this statement in the section explaining the basics of scanning electron microscopy.</p>
<blockquote>
<p><em>However, the equation breaks down when the electron velocity approaches the speed of light as mass increases. At such velocities, one... | 54 |
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