question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p>Assuming 2.3% per year exponential growth of human energy consumption (so, roughly speaking, that corresponds to multiplying consumption tenfold every century), it's argued that human annual energy consumption would be equal to annual solar energy output in 1400 years time. Is that correct?</p>
<p>For reference, hu... | g12771 | [
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<p>Let a,b be two charged particles.
$$\vec{r}_a(0)=\vec{0}$$ $$\vec{r}_b(0)=r\hat{j}$$ $$\vec{v}_a(t)=v_a \hat{i}$$ $$\vec{v}_b(t)=v_b\hat{j}$$</p>
<p>In which both $v_a$ and $v_b$ $<<c$.</p>
<p>Then </p>
<p>$$\vec{E}_{ab}(0)=\frac{q_a}{4\pi \epsilon r^2}\hat{j}$$</p>
<p>$$\vec{B}_{ab}(0)=\frac{\mu q_av_a}{... | g12772 | [
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<p>Can anyone explain to me Hamiltonian mechanics relation to conservation of energy? I'm not very good at mathematics, and I know it's important into understanding Hamiltonian mechanics. However, can it be explained in a simple way?</p> | g12773 | [
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<p>I'm having a hard time to grasp one simple idea.
Let us say we have a moving point charge, q, with velocity v, in the x direction.
Now calculating both the Magnetic and the Electric fields is easy: We know that B=0 in the charge's frame, hence we obtain B in the lab's frame.</p>
<p>Now, let us say we would want to ... | g12774 | [
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<p>It is easy to drink cold drinks, soft drinks with straw but when I tried to drink tea with straw then that was very unpleasant and even for time I lost the sense from my tongue.</p>
<p>My question is why it is difficult to drink hot liquids with straw?(Drinking cold liquids is very pleasant!!!) </p> | g12775 | [
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<p>When you bring a large iron plate and a magnet, the magnet attracts the iron plate and it tends to slide itself to the center. When I place it on the edge, it always aligns at the center why is that?</p> | g12776 | [
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<p>What's the significance of large-scale anomalies in CMB that are confirmed by Planck? I've read somewhere that the cold spots can provide support for string theory or it may be due to a parallel universe . To what extent is that true ? Are there models that can explain these anomalies?</p> | g12777 | [
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<p>Is it possible to calculate the force exerted on a bound, infected red blood cell under various shear stresses? The strength of an adhesive interaction is normally measured by SPR or AFM, however using microfluidics, you can increase the shear stress until the cell dislodges, therefore, can you use this data to calc... | g12778 | [
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<p>In a previous post [ <a href="http://physics.stackexchange.com/questions/57901/">Noether theorem, gauge symmetry and conservation of charge</a> ] we were discussing the different ways to demonstrate the current conservation: via the first Noether theorem applied to a global $U(1)$ gauge symmetry, or via the covarian... | g12779 | [
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<p>I am currently working out the energy required to create a particle anti-particle pair from a collision of a proton travelling along the x-direction with an anti-proton which is at rest. The particle has a mass $m_q$.</p>
<p>Conservation of 4-momentum in the rest frame of the target anti-proton ($c=1$):</p>
<p>$p_... | g12780 | [
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<p>I am trying to calculate the field of an infinite flat sheet of charge
(a plain with uniform charge density $\sigma$) using the superposition
principle.</p>
<p>I know that the field of an infinite line charged with uniform charge
density $\lambda$ is $E(r)=\frac{2\lambda}{r}$.</p>
<p>I want to consider the plain a... | g12781 | [
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<p>Light travels with a speed of $3\times10^8{m\over s}$. My question is that was the light initially accelerating or it archived the speed in an instance? If it was accelerating then why it did not accelerate beyond that? </p> | g159 | [
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<p>I was talking with a friend of mine, he is a student of theoretical particle physics, and he told me that lots of his topics have their foundations in statistical mechanics. However I thought that the modern methods of statistical mechanics, for example the renormalization group or the Parisi-Sourlas theorem, come f... | g12782 | [
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<p>A charged disk or sphere will create currents around its turning axis if a rotation is added. The total current can then be calculated by adding all concentric currents together. Every current (I take the example of a thin charged disk, as it is the most easiest casus) is as big as:</p>
<p>$$
dI = dQ / dt = f*\sigm... | g12783 | [
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<p>For an electronics experiment, I began wondering about the <strong><a href="http://en.wikipedia.org/wiki/Hot_plate" rel="nofollow">electric hot-plates</a></strong> (specifically the temperature dependence over time). If I were to measure the given temperature over time, I assume that the temperature would <em>not</e... | g12784 | [
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<p>Basic facts: The <a href="http://en.wikipedia.org/wiki/TauTona_Mine">world's deepest mine</a> is 2.4 miles deep. Railguns <a href="http://en.wikipedia.org/wiki/Railgun">can acheive a muzzle velocity</a> of a projectile on the order of 7.5 km/s. The Earth's <a href="http://en.wikipedia.org/wiki/Escape_velocity">esc... | g464 | [
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<p>I've read a few explanations about why stress concentration occurs at sharp corners but I don't find the explanations intuitive.</p>
<p>Can anyone explain it perhaps using an analogy such as atoms "holding hands" with neighbor atoms or a similar easy to understand analogy?</p>
<p>Most explanations I've shown just ... | g12785 | [
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<p>Is there any book you recommend for graduation exam/higher studies? I have an exam on physics this week so I need some books to brush up my knowledge. Is there any book you recommend for that purpose? Other than Nelsons Parker Physics.
What I ment here is a book which has all in one <strong><em>like</em></strong> ... | g98 | [
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<p>I'm making several assumptions, not sure if any are correct:</p>
<ul>
<li>there is a black hole at the center of a galaxy</li>
<li>the black hole is eating the galaxy</li>
</ul>
<p>Eventually the galaxy will be gone, right?</p>
<p>Has this been observed? Do we know what happens afterwards?</p>
<p>Posting here si... | g405 | [
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<p>Considering that on the atomic level objects consists of densely spaced positively and negatively charged particles, does not the acceleration of those objects lead to Bremsstrahlung of those particles? And although the monopole field is zero, couldn't higher order multipole radiation escape and cause the inertia? I... | g12786 | [
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<p>I need to estimate a drag race quarter mile time given the car's weight, <a href="http://en.wikipedia.org/wiki/Brake_horsepower#Brake_horsepower" rel="nofollow">bhp</a> and preferably the drive (FWD, RWD, <a href="http://en.wikipedia.org/wiki/Four-wheel_drive" rel="nofollow">4WD</a>). I know $v(t) = ds/dt$ and $a(t)... | g12787 | [
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<p>My question is about two equations regarding uniform spheres that I've run into:</p>
<p>$V=\frac{GM}{r}$</p>
<p>... and ...</p>
<p>$U = \frac{3}{5}\frac{GM^2}{r^2}$</p>
<p>$V$ is unknown to me, and is described (in Solved Problems in Geophysics) as "the gravitational potential of a sphere of mass M." I also fou... | g12788 | [
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<p>I am trying to figure out why vibrations (say, from an engine) loosen screws. It seems to me that there is evident symmetry between loosening and tightening a screw. I am wondering what breaks this symmetry.</p> | g12789 | [
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<p>Why uniform constant magnetic fields can not exert net force on a piece of iron whatever strong it might get?</p> | g12790 | [
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<p>Apparently, light is just a certain wavelength, or "the visible spectrum" of electromagnetic waves. If I recall correctly, my physics teacher explained to me that electromagnetic waves are basically consisted of two, interchanging parts. The "electric" and the "magnetic" parts of the wave are somehow manifesting ea... | g92 | [
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<p><strong>Just wondering:</strong></p>
<p>We know that, in its current form of the $SU(2)_L\times U(1)$, the electroweak theroy rides a wave of huge success. However, is it not possible that the correct <strong>simple</strong> group unification could reveal physics that the current model doesn’t? </p>
<p>For exampl... | g12791 | [
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<p>I'm here asking about real or though experiments (i.e., physical effects) where, at least in principle, one can see some consequence of a non-Lorentz-invariant vacuum state in an otherwise Poincare invariant theory.</p>
<p>Let me develop the question. Assume a theory in which the Hamiltonian (that closes Poincare a... | g12792 | [
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<p>I've seen electromagnetics formulated in the potentials ($\bf A$, $\varphi$) (and their magnetic counterparts) in the Lorenz gauge for a long time. Justifications for using these include that they are less singular than the fields ($\bf E$, $\bf H$) and reduce the redundancy of Maxwell's equations. All the fields ... | g12793 | [
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<p>How can we determine during a lunar eclipse whether the earth moves faster or the moon using minimum instruments?</p> | g12794 | [
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<p>I didn't know where to begin with this problem. I eventually found a solution online, which is why I'm reposting this question with an answer. I was wondering if anyone can explain the one question I have.</p>
<p>A self-contained machine only inputs two equal steady streams of hot and cold water at temperatures $T_... | g12795 | [
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<p>I have currently been working with a sample that "appears to" decrease its resistance when I cover it and protect it from light.</p>
<p>Basically it presents the opposite behaviour of a photoresistor.</p>
<p>What kind of phenomenon may cause this? Or it has to be a measurement error?</p>
<p>EDIT: I am talking abo... | g12796 | [
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<p>When I studied physics some time ago my teacher explained that if we consider the gravitational atraction not instantaneous, such as the General Relativity says, the planets would be attracted towards the position were other planets were before and not the current one, getting spiral orbits instead of ellipses.</p>
... | g12797 | [
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<p>In General Relativity, if the system accelerates, the inside of the system and the outside of the system will have different speed of time.</p>
<p>Where is the boundary of the system? </p>
<p>If a human accelerates closer to the speed of light, does that mean the human exist inside of their specific system? </p> | g12798 | [
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<p>The concept of relativistic energy comes from it's conservation in relativistic mechanics for an elastic collision.</p>
<p>It seems to me that another possible derivation could equate the energy of a single particle before, with the kinetic energy after of N particles after the energy is distributed amongst them in... | g12799 | [
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<p>Why is it that the distance between two light rays changes as they pass from one material to another? </p>
<p>It must have something to do with the change in refractive index, but to me it seems the ''ends'' of the beam are refracted by equal amounts. </p>
<p>Can you explain this? See the picture below.</p>
<p... | g12800 | [
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<p>I am having a hard time in finding out what exact light media laser shows use. I am trying to build a laser show myself. I know that the laser light is reflected off these particles in such a way that that it makes the laser line "viewable" in <em>all directions</em></p>
<p>Can somebody explain to me how exactly do... | g12801 | [
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<p>D'Alembert's principle suggests that the work done by the internal forces for a virtual displacement of a mechanical system in harmony with the constraints is zero.</p>
<p>This is obviously true for the constraint of a rigid body where all the particles maintain a constant distance from one another. It's also true ... | g12802 | [
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<p>The equation describing the force due to gravity is $$F = G \frac{m_1 m_2}{r^2}.$$ Similarly the force due to the electrostatic force is $$F = k \frac{q_1 q_2}{r^2}.$$ </p>
<ol>
<li><p>Is there a similar equation that describes the force due to the strong nuclear force? </p></li>
<li><p>What are the equivalent of m... | g12803 | [
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<p>In "The Elegant Universe," two individuals, George and Gracie, are noted to be moving relative to one another in space and wearing clocks. They sync their clocks upon passing each other. Each observes the other's clock to be ticking more slowly. Gracie communicates with George via cell.</p>
<blockquote>
<p>Gracie... | g12804 | [
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<p>It is written everywhere that gravity is curvature of spacetime caused by the mass of the objects or something to the same effect. This raises a question with me: why isn't spacetime curved due to other forces or aspects of bodies?</p>
<p>Why isn't it that there are curvatures related to the charge of a body or the... | g366 | [
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<p>I was talking with a friend recently about concave mirrors, which frequently invert the reflected image - I think we were playing with a spoon. I raised the question, if you had a mirror whose shape could be easily controlled so you could move it from convex through being flat to being concave, at what point does th... | g12805 | [
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<p>Imagine a manifold $\mathbb{R}^{1,3}\times{}B$ where $B$ is a compact group-manifold with isometry group $U(1)\times{}SU(2)\times{}SU(3)$.</p>
<p>Let's consider the Dirac equation for a massless Spinor field.</p>
<p>$iD_{1+n}\Psi=0$</p>
<p>and separating the compact space part with the 4-space part</p>
<p>$i(D_4... | g12806 | [
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<p>The nerve impulse transmission is specifically a biophysical process. Under a <em>resting</em> stage, the membrane is already polarised (presence of charge on either side leading to a potential difference across it, due to its finite capacitance). Changes in this polarisations mediated by several agents, cause some ... | g12807 | [
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<p>I'm trying to better understand the modal content and dynamics of laser cavities. I'm specifically interested in mode-locking, although this question is pretty general and applies to CW lasers too.</p>
<p>I understand that the modal spacing, Δf, in a cavity is set by cavity geometry and the gain bandwidth, ΔF, is s... | g12808 | [
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<p>Let $\Omega$ be an observable and let $\Psi = \sum a_i\phi_i$ be a decomposition of a state of a system (satisfying the Schrödinger equation) in eigenfunctions of $\Omega$ (assume for simplicity it is a finite linear combination and there is no degeneracy). Measuring the observable $\Omega$ will give the value $\lam... | g12809 | [
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<p>I'm reading Peter Atkins' book, <em>Galileo's Finger</em>, and in the chapter on energy, he makes the points that the conservation of momentum stems from the shape of space (that it's smooth and not lumpy) and that the conservation of energy stems from the shape of time (that it's smooth and not lumpy). I'm not tota... | g12810 | [
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<p>I got this question from playing games like Halo and Borderlands (I know kinda dumb but raised a good question) in which the primary protection is an electric shield. Now I'm wondering if it would be possible to use energy to create a barrier in which physical objects either get disintegrated or deflected. Id imagin... | g12811 | [
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<p>This is an approach to anomalies which seems unfamiliar to me..</p>
<ul>
<li><p>Firstly what is this function $W$ which seems to satisfy the equation, $\frac{\partial W }{\partial g^{\mu \nu} } = \langle T_{\mu \nu} \rangle $. Is there any standard such $W$? </p></li>
<li><p>Now one says that this $W$ must satisf... | g12812 | [
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<p>Initially at time $t=0$, a solid sphere slides with velocity $v$ along a horizontal surface. The coefficient of friction is u. Find the required time for the sphere to stop sliding (the sphere will then be rolling). </p>
<p>Ive tried using Newtons equations of motion but I'm not sure what the final velocity will be... | g12813 | [
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<p>Let's assume we have a 1 kg cube on a flat uniform surface. The coefficients of friction between them are $\mu_k = 0.25$ and $\mu_s = 0.50$. This cube is moving at 1 m/s in the y direction, with whatever force is needed to overcome friction being applied. There is no force or motion in the x direction. Assume $g... | g12814 | [
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<p>If a particle is placed on a rotating turntable then the particle has a tendency to slip tangentially with respect to the underneath surface... So the friction should act tangentially to the particle... Why then does it act towards the center... Please explain with respect to inertial frame</p>
<p>Friction opposes ... | g64 | [
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<p><img src="http://i.imgur.com/EAVEwED.png" alt="HW Problem"></p>
<p><strong>1.) What is the acceleration of the hanging mass? (Indicate the direction with the sign of your answer.)</strong></p>
<p><strong>2.) Determine the tension in the cord. (Indicate the direction with the sign of your answer.)</strong></p>
<p>... | g12815 | [
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<p>I'm having trouble understanding how Carroll (Spacetime and Geometry p.296) explains the effect of a passing gravitational wave on test particles.</p>
<p>If we have two geodesics with tangents $\vec{U}$, $\vec{U'}$ that begin parallel and near each other, and $\vec{S}$ is a vector connecting one geodesic to another... | g12816 | [
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<p>For two non-interacting particles, with eigenfunctions $\phi_{n1}(x1)$ and $\phi_{n2}(x2)$ in a one-dimensional potential well $V_{(x)}$ with n = 1,2,....</p>
<p>Consider two spinless non-identical particles:</p>
<p>What is the degeneracy of the ground state and first excited state?</p>
<p>I'm thinking it should ... | g12817 | [
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<p>In "Mechanics" book by Landau and Lifshitz, $\S18$ "Scattering", problem 7 on deducing the form of scattering field given the effective cross-section as a function of scattering angle an equation is obtained:</p>
<p>$$-\pi\text{d}\log w=\text{d}\left(\frac s w\right)\int_0^{s^2/w^2}\frac{\chi'(x)\text{d}x}{\sqrt{\f... | g12818 | [
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<p>I was wondering if a photon is divisible. </p>
<p>If you look at a photon as a particle, then you may be able to split it (in theory).</p>
<p>Is it possible and how do you split it?</p> | g602 | [
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<p>I wanted to know the importance and applications of the study of the diatomic molecule in physics</p>
<p>I know that the question may not make much sense to you, but while exposing the solution of relative motion of the diatomic molecule, some students asked me about their applications and could not answer. On the ... | g12819 | [
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<p>This is related to my previous Phys.SE <a href="http://physics.stackexchange.com/q/52894/2451">question</a> on the derivation of the phase function - upon sifting and scanning through 600 pages of John Strutt's collected work, there is <strong>absolutely no mention</strong> of Rayleigh's phase function (related to <... | g12820 | [
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<p>Suppose I have two plates with a viscous fluid in between. I slide them in the same direction (a direction in their own plane), one at $5 \,\text{m/s}$ and the other at $6 \,\text{m/s}$. Due to the relative velocity, there will be a viscous damping force tending to equalize the velocities of the plates.</p>
<p>Now ... | g12821 | [
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<p>If the earth is rotating at some <a href="https://en.wikipedia.org/wiki/Earth%27s_rotation#Angular_speed" rel="nofollow">$465~\text{m}/\text{s}$</a> at the equator and that's really fast.</p>
<ol>
<li>Shouldn't we in that case be in orbit with the earth just not fast enough? </li>
<li>How fast do we need to move?</... | g12822 | [
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<blockquote>
<p><em>Two straight ladders, AC and BC, have equal weights $W$. They stand in equilibrium with their feet, A and B, on rough horizontal ground and their tops freely hinged at C. Angle CAB = 60$ ^o$, angle CBA = 30$^o$ and AB = $l$ (see diagram). Find the vertical reactions at A and B.</em></p>
</blockquo... | g12823 | [
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<p>If I have a system consisting of 2 Einstein solids (<code>A</code> and <code>B</code>) is it equivalent to say that maximizing the multiplicity of the system is the same as setting the temperature to $\infty$? I have two reasons to support this Idea.</p>
<p>1) The total multiplicity of the system can be expressed a... | g12824 | [
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0.006126977503299713,
0.00... |
<p>I have a very naive question about the notion of time-reversal symmetry applied to topological insulators that are studied in experiments. If I understand correctly, the exsistance of time-reversal symmetry is crucial for the occurence of topologically protected surface states in topological insulators. At least t... | g12825 | [
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<p>I read this example in a popular math book I was browsing, and the author does not give any physical explanation. </p>
<p>The example: Consider a rock falling freely under gravity. There are no viscous or dissipative effects. We will find the average speed at the end of 5 seconds.</p>
<p><strong>Time-domain.</stro... | g12826 | [
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0.059... |
<p>Suppose I look at a parallel plate capacitor in its rest frame and calculate the electrostatic energy, $E$.</p>
<p>Next, I look at the same capacitor in a primed frame boosted in the direction perpendicular to the plane of the plates. In this frame, the $E$-field is the same strength, there is no magnetic field, an... | g12827 | [
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<p>Let's say I turn on a <a href="http://en.wikipedia.org/wiki/Van_de_Graaff_generator" rel="nofollow">Van de Graaff</a> which creates a large positive charge. Now let's say I have an object with a positive charge in my hand and I start walking toward the Van de Graaff from $x$ meters away. If I walk an arbitrary dista... | g12828 | [
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0.008313496597111225,
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<p>Suppose we have some tensor with components $T^{ij}$. Then suppose that we also have $T_{ij}$. </p>
<p>When would $T^{ij}T_{ij} = (T^{ij})^2 = (T_{ij})^2$?</p> | g12829 | [
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<p>A month or two ago I purchased a “Skywatcher Explorer 130P Newtonian Reflector” telescope - which so far is brilliant when looking at the Moon, esp. using a neutral density filter. However, when looking at Venus or Mars - which are very easy to view and beautiful to see through the eyepieces - they seem slightly blu... | g499 | [
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<p>I am trying to find a formula that will enable me to calculate the illumination of the moon down to one thousandth of a percent, given that the Gregorian year, month, day, and hour is known. Can anyone help me with this formula?</p> | g12830 | [
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<p>We know that each gas giant planet was warmest when it was young. This warmth came from <a href="http://en.wikipedia.org/wiki/Internal_heating" rel="nofollow">internal heating</a> from both radioactive decay and from gravitational potential energy. This warmth, in turn, means that the planet emits blackbody flux.</p... | g12831 | [
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<p>I'm busy studying for my Physics exam this evening and I've come across a vector problem that I cant quite solve. Any help would be appreciated!</p>
<p>We are given the following vectors:</p>
<pre><code>A = 5i - 6.5j
B = -3.5i + 7j
</code></pre>
<p>We are also told that a vector C lies in the xy-plane and is perp... | g12832 | [
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<p>I'm tutoring high school students. I've always taught them that:</p>
<blockquote>
<p>A charged particle moving without acceleration produces an electric <em>as well as a magnetic field</em>.</p>
</blockquote>
<p>It produces an electric field because it's a charge particle. But when it is at rest, it doesn't prod... | g346 | [
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<p>I know I've seen zodiacal light, especially at my old club's best dark-site. However, I'm pretty sure I've yet to see the <a href="http://en.wikipedia.org/wiki/Gegenschein" rel="nofollow">gegenschein</a>. How good does the seeing have to be to be able to see that?</p> | g12833 | [
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<p>Here is a typical question which I have been asked many times while giving public lectures in various places. While I know one of the paths like Diploma, Masters and PhD but sometimes this is not so obvious for that eager young person who thinks to go on that path. So what that would be?</p> | g12834 | [
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<p>I remember a method to make a reasonable estimate of the magnitude of a given star X by using two other stars of known magnitude as references. The method used evaluation phrases like "the star X and the reference star appear to have the same brightness, and this sensation remains even after prolonged observation" o... | g12835 | [
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<p>Lets consider it case by case:</p>
<p>Case 1: Charge particle is at rest. It has electric field around it. No problem. That is its property.</p>
<p>Case 2: Charge particle started moving (its accelerating). We were told that it starts radiating EM radiation? Why? What happened to it? What made it do this? </p>
<... | g437 | [
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<p>I am looking at peltier heaters/coolers, and all of them are thin wafers like the one pictured below.</p>
<p><img src="http://i.stack.imgur.com/zZBXg.jpg" alt="Peltier device"></p>
<p>This works fine for some things (ie. a microchip or a beer coaster) but not for others (ie. anything elongated). Assume, for the sa... | g12836 | [
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... |
<p>Here goes: </p>
<ul>
<li>imagine a spacecraft with engines shut off in a free fall towards some celestial body x.</li>
<li>let's say the distance to surface is $100 000$ $\text{meters}$. </li>
<li>initial vertical velocity is $500$ $\text{m/s}$. </li>
<li>gravitational pull experienced by the body is obviously give... | g406 | [
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<p>We normally think of the "default" or "root" state of things as being on the positive side of the spectrum. For example, we don't normally use a <code>+</code> symbol to indicate the sign of positive numbers, whereas negative numbers are invariably preceded with <code>-</code> to indicate their negative sign. Simi... | g258 | [
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<p>When I boil water in the kettle, it makes a nice cup of tea. Sometimes I need to use a microwave because a kettle isn't available. I boil the water in the mug and it looks pretty normal, but when I drop in the teabag the water froths up and looks foamy. I don't see what the chemical difference is here, so I assum... | g12837 | [
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<p>I am a visual person, so it's hard to imagine the information I keep getting, but shouldn't time be a constant? </p>
<p>If you were traveling at the speed of light and your able to cover $299{,}792{,}458$ meters in one second, aren't you just going faster than anything else? Why does time slow down as you approach ... | g12838 | [
0.07224346697330475,
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0.04837395250797272,
... |
<p>We know that the sun loses an amount of it's mass equivalent to the amount of energy it produces, according to the E=mc² equation.
so the sun is losing mass every second. Does this affect the space-time curvature it creates. Or does this affect the distance between the sun and the Earth. Does losing mass affects the... | g12839 | [
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<p>Suppose we meet a person wearing glasses.<em>Can we determine whether the person is short-sighted or long-sighted</em>?</p>
<p>However,due to courtesy,we are not allowed to ask him to try the glasses and in general we can't even make any mention of them.</p>
<p><strong>Attempt at the solution:</strong>
I tried usi... | g12840 | [
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0.05022... |
<p>I have a very basic question about photons in double-slit experiment. I am not good at math, and have some Quantum mechanics knowledge. Math free explanation would be very good to me.</p>
<p>When we do double slit experiment with single photon at a time, it will be detected at some location of screen. Over the time... | g12841 | [
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<p>Water inside bucket is rotated (by spoon or something) to flow in circular motion. An object kept in the bucket tends to be at the center of the bucket. Why is that?</p> | g196 | [
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<p>From my limited understanding of quantum entanglement, it seems like qubits act the same way as pseudo-random-number-generators (except as far as we can tell, these ones really are random). When you entangle two qubits, you give them both the same seed.</p>
<p>Then a measurement is like running an (otherwise deter... | g12842 | [
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... |
<p>Coherent states of light, defined as</p>
<p>$$|\alpha\rangle=e^{-\frac{|\alpha|^2}{2}}\sum_{n=0}^\infty \frac{\alpha^n}{n!}|n\rangle$$</p>
<p>for a given complex number $\alpha$ and where $|n\rangle$ is a Fock state with $n$ photons, are usually referred to as the most classical states of light. On the other hand,... | g12843 | [
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0.05047938972711563,
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0.0074987150728702545,
0.034... |
<p>Suppose that I escaped the gravitational field of earth.</p>
<p>Then: am I going to be pulled by Sun's gravity?</p> | g12844 | [
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... |
<p>In QFT one may refer to a particle as a representation of the Lorentz group (LG). More accurately - every particle is a quantum of some field $\phi(x)$ that belongs to some representation of the LG. <em>I wonder if that is really neccesary?</em> Arguments are usually like following:</p>
<p>Let $L$ be some Lorentz t... | g12845 | [
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0.0... |
<p>What's the scattering matrix for a PBS (polarization beam splitter) ?
Is it just unitary ?
If one polarization never couples into another polarization (then there's a lot of zeroes in that 4x4 matrix) - is that impossible somehow ?</p> | g12846 | [
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0.01514086127281189,
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-0.082184... |
<p>In <a href="http://physics.stackexchange.com/questions/6209/paradoxical-interaction-between-a-massive-charged-sphere-and-a-point-charge">PSE here</a> electrons are added to a sphere and gravitational modifications are expected. </p>
<p>My question is:<br>
Is there any <strong>experiment</strong> that show that a n... | g12847 | [
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0.023465944454073906,
-0.00... |
<p><a href="http://en.wikipedia.org/wiki/Tolman_surface_brightness_test" rel="nofollow">http://en.wikipedia.org/wiki/Tolman_surface_brightness_test</a></p>
<p>It says:</p>
<blockquote>
<p>In a simple (static and flat) universe, the light received from an object drops inversely with the square of its distance, but t... | g12848 | [
0.004816910717636347,
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<p>In hydrodynamics of an ideal, non-compressive flow we use 5 variables: pressure $p$, density $\rho$ and velocity field $\mathbf{v}$. So we need 5 equations. Landau's "Hydrodynamics" states that the equations are:</p>
<ol>
<li><p>The mass continuity equation $\frac{\partial \rho}{\partial t}+\nabla (\rho \mathbf{v})... | g12849 | [
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0.012909991666674614,
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... |
<p>How is the image in a mirror created without a lens or pinhole?</p>
<p>From every point in the world there are infinitely many rays going out.
How come the image on a mirror is ok, when there is no pinhole to capture
exactly one ray from each world point, or a lens to focus all rays coming
from one world point onto... | g12850 | [
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<p>How is the image in a mirror created? Are there infinitely many light rays?</p>
<p>My motivation for the question is from image processing.
We work with images as discrete 2D functions, as matrices.
Spatial sampling is done, and also quantization.
Then I thought, well that is far from perfect, I wonder
how does God... | g12851 | [
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<p>Is there a simple way to explain the difference between a classical and truly quantum correlation to a non-quantum person who has basic understanding classical correlation? </p>
<p>I mean without invoking quantum mechanics, a simple CHSH type Bell inequity can be explained without it--perhaps with a little more mat... | g12852 | [
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<p>I hope you can clear up my following confusions.</p>
<p>In Girardello's and Grisaru's paper (Nuclear Physics B, 194, 65 (1982)) where they analysed the most general soft explicit supersymmetry breaking terms, they explicitly mentioned that $\mu \psi \psi$ is not soft, where $\psi$ is the fermionic component of a sc... | g12853 | [
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<p>On earth, using <a href="http://en.wikipedia.org/wiki/Earth_sheltering">earth-sheltering</a> techniques can significantly reduce the temperature fluctuations on a structure. Would the same statement be true as well on the Moon? Does the Moon's core still contain significant heat?</p> | g12854 | [
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<p>Assuming we originated from a single infinitely dense point in space time in the big bang, how can there be parts of the universe that we can't see as the light has not reached us yet, if nothing can travel faster than the speed of light relative to our frame of reference? Is that because the universe can expand fas... | g10 | [
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<p>I can find various speeds and estimated durations listed at numerous places but none specifically describe the frame of reference. </p>
<p>Possible options as example of kind of answer I expect. </p>
<ul>
<li>Local Galactic cluster </li>
<li>Distance quasars </li>
<li>The cosmic background radiation?</li>
</ul>... | g12855 | [
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