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<p>It seems to be common consensus that the world is non-deterministic and this is <em>proved</em> by <a href="http://en.wikipedia.org/wiki/Bell%27s_theorem#Overview">Bell's theorem</a>.</p>
<p>But even though Bell's experiments proved that the theory of quantum mechanics work, How does it prove the non-existent of <a... | 6,103 |
<p>I am reading the paper <a href="http://cds.cern.ch/record/133713/files/" rel="nofollow">Fundamental monopoles and multimonopole solutions for arbitrary simple gauge groups - Weinberg, Erick J</a> .</p>
<p>In appendix C of this paper the author states, that the solution obtained (eqn 2.20) by embedding a SU(2) bps m... | 6,104 |
<p>I've been studying electroweak theory and you need to keep the Lagrangian covariant by introducing covariant derivatives. What is a covariant derivative? And what does it mean to keep the Lagrangian covariant?</p>
<p>Also, in electroweak symmetry breaking, the gauge bosons attain their masses via the action of a 'c... | 6,105 |
<p>I know that momentum and energy are always conserved in collisions, but if we have a perfectly inelastic collision in which an object sticks to another object $m_1 v_1 + m_2 v_2 = (m_1+m_2)v_{12}$, the kinetic energy is not conserved. I know that kinetic energy converts into thermal or sound energy, but I don't see ... | 213 |
<p>I recently came across the definition of the Center of Mass of a system as the point about which the <strong>first</strong> <em>moment of mass</em> is zero.</p>
<p>Further, it defined <a href="http://en.wikipedia.org/wiki/Moment_of_inertia" rel="nofollow">Moment of Inertia</a> as the <strong>second</strong> <em>mom... | 6,106 |
<p>I have an electric motor that can apply a pull force of $3000 \;\mathrm{lb}$ (electric winch), it draws $180 \;\mathrm{A}$ at $12 \;\mathrm{V}$.</p>
<p>I understand that power $P = I \cdot V = 2.1 \;\mathrm{kW}$. If I know the time this motor was running I can figure out the energy using $E = P \cdot t$. Why not us... | 6,107 |
<p>The experiments of innovative Faraday and Joseph Henry in USA, conducted around 1830, demonstrated conclusively that electric currents were induced in closed coils when subjected to changing magnetic fields. </p>
<p>Maxwell developed a set of equations describing the laws of electricity and magnetism. Using these ... | 6,108 |
<p>Dark Matter appears to have more in common with phenomena related to spatial geometry then a particle. I thought in General Relativity, space can be curved without the presence of matter so gravitational lensing does not imply there is matter present but that the space in a region is curved. If Dark matter has mor... | 6,109 |
<p>I'm asked to find the linear acceleration of this object</p>
<p><img src="http://i.stack.imgur.com/zFdHp.jpg" alt="enter image description here"></p>
<p>for a given tension $T$ knowing that both discs have mass $M$ and we don't consider the mass of the bar.</p>
<p>The answer of the book is different than mine and... | 6,110 |
<p>I was watching the speed skating event, and was wondering, why do the athletes use their right hand while accelerating? If they want to increase the moment of inertia, then they should move the hand away from themselves, but they don't do that.</p>
<p>Is it due to the shifting of the Centre of Gravity to the right ... | 6,111 |
<p>Does anyone knows a simple way to understand why the average value of the creation (or annihilation) operator should be equal to zero in the Canonical Ensemble? Why instead if I'm dealing with a Grand-Canonical ensemble the same averages can be different from zero? </p>
<p>I'm asking this because in the Bogoliubov ... | 6,112 |
<p>Why can't solar panels produce 1 Kw per 1 square meter? This is the energy of the Sun's radiation per square meter on Earth but solar panels don't come close. Why can't we trap all that energy? Where is the rest of the energy going?</p> | 6,113 |
<p>If I have a volume of $L$ liters of salt water at a concentration of $\approx N$ mM NaCl and I pour it into an electrophoretic apparatus (like this one: <img src="http://upload.wikimedia.org/wikipedia/commons/a/a6/Gel_electrophoresis_apparatus.JPG" alt="image">). Once we turn the apparatus on, and set the power lev... | 6,114 |
<p>I have a large cylinder made of a rigid thick plastic with a speaker inside of it. I want to be able to hear high pitched / high frequency noise from the outside but I'm primarily hearing bass. The treble is muffled. What can I do to be able to hear crisp sound from the outside? How should I modify the cylinder or s... | 6,115 |
<p>How do scientists discover <a href="http://en.wikipedia.org/wiki/Superconductivity" rel="nofollow">superconductors</a>? Do they test properties of every material available on Earth? Or do they do something mathematically?</p> | 6,116 |
<p>How can the Anomalous Expansion of Water from 4$^\circ$C to 0$^\circ$C be explained with reference to subatomic particles?</p> | 6,117 |
<p>Is it possible that a metallic object will <em>not</em> be under the influence of a magnetic field at a certain <em>closeness</em> to a conductor, but will then experience the effect on moving to a particular distance (and onwards)? In other words, is there a threshold radius around a conductor <em>within</em> which... | 6,118 |
<p>Exist some relationship between irradiance units and wavelength of the incident sunlight?
What about irradiance? I want to establish a relationship between wavelength and irradiance, because I would try to model photosynthesis on Vensim. </p> | 6,119 |
<p>What is the maximum frequency of the Gamma Rays produced during supernovae? And how are these detected by telescopes without getting some serious damage done?</p> | 6,120 |
<p>I was wondering whether the rotational speed of a discus has any influence on the flight of the discus. Would slowing the rotation or speeding it up change the trajectory in any way or would the flight simply become unstable when slowing down?</p> | 6,121 |
<p>What exactly is the difference between 2-Level, 3-Level and 4-Level systems? Why can we not achieve stimulated emission in a two-level system using optical pumping?</p> | 6,122 |
<p>How can we theoretically calculate the boiling point of water at given pressure (other subtle parameters as well, if any)? What is the most accurate (minimum discrepancy with experimental value) computation that can analytically predict the
boiling point of water?</p>
<p>Possibly we need to invoke quantum mechanics... | 6,123 |
<p>When we say Laser transverse modes. Is that mean what we will get at the output spot of laser beam ? secondly In practice , what TEM01 or TEMnm means ?</p>
<p><img src="http://i.stack.imgur.com/F6s7q.jpg" alt="enter image description here"></p> | 6,124 |
<p>The property of hermitian is the sufficient condition for eigenvalue being real.
Is there any non-hermitian operator on Hilbert Space with all real eigenvalues? If there exist, then can all eigenstates be orthogonal to each other? And these operators have any application in Quantum mechanics? </p> | 6,125 |
<p>I heard from Prof. Katrin Becker (in her "SUSY for Strings and Branes - Part 1" lecture) that the classical $SL(2,\mathbb{R})$ symmetry in type IIB String theory becomes $SL(2,\mathbb{Z})$ in Quantum because of charge quantization. However, I cannot see how does it work. Is there any rigorous Mathematical derivation... | 6,126 |
<p>Assume I use a coil to create B-flux and put ONE Neodymium cylinder magnet (1"diameter & 0.25" thick) close to the flux, it would create 10 lbs force. Does it mean that I put TWO cylinder magnets (1"diameter & 0.25"+0.25" = 0.5" thick) would create 20lb force? </p> | 6,127 |
<p>So I'm in grade 10 but I finished all my physics classes, maths and further maths (Calculus). I would like to start with some harder stuff (university physics). What books do you recommend for both maths and physics? And if possible what steps should I take?</p> | 98 |
<p>This is from the beginning of Srednicki's QFT textbook, where he writes (approximately): </p>
<p>In QM we associate a unitary operator $U(\Lambda)$ to each proper orthochronous Lorentz transformation $\Lambda$. These operators must obey the composition rule </p>
<p>$$U(\Lambda'\Lambda) = U(\Lambda')U(\Lambda).$$</... | 6,128 |
<p>How exactly does a battery produce a current in the circuit connected across its ends? I dont want to know the chemical reactions in the battery core, but just the essence of it. I believe it doesn't do this by creating an excess of electrons at the -ve terminal and a deficit at the positive terminal. Moreover, how ... | 6,129 |
<p>To our time a light year is the distance that light travels in a vacuum but if we consider time of observer which moves at speed of light we found for light time and distance doesn't really exist.
Does distance really exist?</p>
<p>($d\tau=dt\gamma^{-1}$ where the at speed of light $\gamma^{-1}=0$)</p>
<p>isn't u... | 195 |
<p>I'm new to this forum so I hope this post falls under the guidelines of what's acceptable.</p>
<p>I'm currently finishing my grade 11 year of high school and I have hopes of attending one of the prestigious schools in the US such as MIT, Harvard, Stanford, Princeton, etc. I would love to be able to study physics in... | 98 |
<blockquote>
<p>Two people, Micah and Lyra, with different near points are equally
close to an object. Both inspect the object through the same magnifier
by holding the lens close to the eye. Micah's near point is located
farther away from his eye than Lyra's near point is located relative
to her eye. Micah w... | 6,130 |
<p>The following is the question that very commonly appears in all HS textbooks.<br>
A hollow sphere with a hole is taken to a depth of 40cm when the water starts entering the hole. if the surface tension of water is 70dyne per cm find the radius of the hole.<br>
All the textbooks solve it in a similar manner as given ... | 6,131 |
<p>If you have two particles of the same species , Quantum mechanics says that $\Phi_{m_{1},x_{1},p_{1},m_{2},x_{2},p_{2}}=\alpha\Phi_{m_{2},x_{2},p_{2},m_{1},x_{1},p_{1}}$
But I don't understand why $\alpha$ doesn't depend on $x$ , $p$ . If $\alpha$ depends on $SO(3)$ invariants as $x^2 , x.p , p^2$ etc then it will... | 6,132 |
<p>In an answer to a previous question of mine, <a href="http://astronomy.stackexchange.com/questions/888/are-the-inner-planets-on-planar-orbits-because-there-was-more-dust-in-the-inner-s">one that asked about the planar orbits of inner planets</a>, I was told the following (emphasis mine):</p>
<blockquote>
<p>On th... | 6,133 |
<p>I understand that you get coffee rings on a table as a result of solute migration (solutocapillarity) towards the pinning of the circumference of the coffee ring <a href="http://www.nature.com/nature/journal/v389/n6653/abs/389827a0.html" rel="nofollow">[Deegan et al.]</a>.</p>
<p>Below is an observation that I made... | 6,134 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/25070/why-can-we-see-the-cosmic-microwave-background-cmb">Why can we see the cosmic microwave background (CMB)?</a> </p>
</blockquote>
<p>We all have seen evidence of radiation left from the Big Bang, bu... | 214 |
<p><strong>The actual number:</strong></p>
<p>How far apart are galaxies on average? </p>
<p><strong>An attempt to visualize such a thing:</strong></p>
<p>If galaxies were the size of peas, how many would be in a cubic meter?</p> | 6,135 |
<p>I have written a computer simulation of the driven damped pendulum, pretty much as the one <a href="http://www.cmp.caltech.edu/~mcc/Chaos_Course/Lesson2/Demos.html" rel="nofollow">shown here</a>, only that I did it Python. Next, I have found some parameters for which the pendulum behaves chaotic. Now I want to extra... | 6,136 |
<p>Taking it to the bottom of layman's terms, what would be the shortlist of significant <em>things</em> in the universe?</p>
<p>A list I could think of myself would put</p>
<ul>
<li><strong>Energy</strong> (at whatever wavelength travelling through space)</li>
<li><strong>Gas</strong> (Atoms and molecules floating i... | 6,137 |
<p>I was wandering around the <a href="http://pdg.lbl.gov/2011/tables/rpp2011-sum-mesons.pdf" rel="nofollow">particle date group</a> page for meson and couldn't find a meson for top-bottom, which from symmetry you would expect. </p>
<p>Q1: Is this because it hasn't been found?
Q2: There is an underlying reason why it ... | 6,138 |
<p>The Lorentz force on a charged particle is perpendicular to the particle's velocity and the magnetic field it's moving through. This is obvious from the equation:</p>
<p>$$ \mathbf{F} = q\mathbf{v} \times \mathbf{B} $$</p>
<p>Is there an <em>intuitive</em> explanation for this behavior? Every explanation I've seen... | 6,139 |
<p>I am recently reading Xiao-Gang Wen's paper (http://dao.mit.edu/~wen/pub/edgere.pdf) on edge excitation for fractional quantum hall effect. On page 25, he claimed that it is easy to show that there exist a bijective correspondence between a symmetric polynomial and edge excitation of the fractional quantum hall drop... | 6,140 |
<p>In P.A.M. Dirac's <em>The Principles of Quantum Mechanics,</em> Chapter 10 (Observables), pp. 40, at the end of the chapter there is a proof that I don't understand at all.</p>
<p>Here is a pdf link to the book readable online: <a href="http://www.fulviofrisone.com/attachments/article/447/Principles%20of%20Quantum%... | 6,141 |
<p>I'm trying to derive the equation for work done by a vibrating string, but I'm running into problems. The easiest way - the method used by the other question by this name - makes the approximation $\sin\theta\approx\tan\theta$, that is, the small angle approximation.</p>
<p>I'm fairly sure this doesn't reflect some... | 6,142 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/3158/why-quantum-entanglement-is-considered-to-be-active-link-between-particles">Why quantum entanglement is considered to be active link between particles?</a> </p>
</blockquote>
<p>I am a layman trying... | 61 |
<p>The following is the question from my school.</p>
<p><strong>A source emits sound uniformly in all directions. A radial line is drawn from this source. On this line, determine the positions of two points,
1.00m apart, such that the intensity level at one point is 2.00dB greater than the intensity level at the other... | 6,143 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/937/how-does-gravity-escape-a-black-hole">How does gravity escape a black hole?</a> </p>
</blockquote>
<p>How can gravity get out of a black hole? If a black hole is so powerful that even light does not ... | 215 |
<p>The below explanation why magnetism exists is superb in <a href="http://www.youtube.com/watch?v=1TKSfAkWWN0" rel="nofollow">this video</a>. The explanation about magnets is also great in <a href="http://www.youtube.com/watch?v=hFAOXdXZ5TM" rel="nofollow">this video</a>.</p>
<p>A magnet has atoms with unpaired elect... | 6,144 |
<p>Fission divides one Helium atom into two Hydrogen (Deuterium) atoms. And fusion, once again, puts together those two Hydrogen atoms into one Helium atom. In both reactions, overall output energy is enormous.</p>
<p>$ \begin{array}{rcrclclrl}
\text{1 Neutron} & + & {}_2^4He & \to & {}_1^1H + {}_1^1H ... | 6,145 |
<p>I think it's about time for me to ask this question, as I've been contemplating this for a while.</p>
<p>$$E = mc^2.$$</p>
<p>This is Einstein's most famous equation. But what does it mean?</p>
<p>On my own, I had to think a lot about it, since no one in my close surroundings can give me good answers. </p>
<p>To... | 6,146 |
<p>In Morii, Lim, Mukherjee, <i>The Physics of the Standard Model and Beyond.</i> 2004, ch. 8, they claim that the Peskin–Takeuchi oblique parameters <i>S, T</i> and <i>U</i> are in fact Wilson coefficients of certain dimension-6 operators. On page 212, they claim that the <i>T</i> parameter is described by
$$O_T=(\ph... | 6,147 |
<p>I'm currently reading an online article, and below is a quote from that article:</p>
<blockquote>
<p>The thermodynamic entropy to change $n$ memory cells within $m$ states is $ΔS=k_B\ln(m^n)$, where $k_B$ is the Boltzmann constant. From the second law of thermodynamics, $ΔS=\dfrac{ΔQ}{T}$, where $ΔQ$ is the energ... | 6,148 |
<p>A gauge field is introduced in the theory to preserve local gauge invariance. And this field (matrix) is expanded in terms of the generators, which is possible because the gauge field is traceless hermitian. </p>
<p>Now why did we choose it as traceless Hermitian? What was the insight behind the choice that made us... | 6,149 |
<p>This is a practice Physics Subject GRE problem.</p>
<blockquote>
<p>A parallel-plate capacitor has plate separation $d$. The space between the plates is empty. A battery supplying voltage $V_0$ is connected across the capacitor, resulting in electromagnetic energy $U_0$ stored in the capacitor. A dielectric, o... | 6,150 |
<p>I suspect a valid scientific, physics answer for this question, because I'd venture that train, insurance companies would've calculated and contemplated this question. </p>
<p>Yet the train headlights at <a href="http://www.youtube.com/watch?v=0TY9Kdj5PJI" rel="nofollow">http://www.youtube.com/watch?v=0TY9Kdj5PJI</... | 6,151 |
<p>can we by any means amplify magnetic signal as we can with electric signal. As both electric and magnetic field can be represented in the form of a wave the analogy seems to be natural. </p>
<p>I want the input and output as magnetic signal. </p> | 6,152 |
<p>This question is in reference to the paper,
<a href="http://arxiv.org/abs/1301.7182" rel="nofollow">http://arxiv.org/abs/1301.7182</a></p>
<ul>
<li><p>What exactly is the argument being made on page 6 and 7? </p>
<p>One deduces that the function $\Delta$ has to be such that, $\Delta^2(k,\tau) = \Delta^2(\frac{k}{... | 6,153 |
<p>I wonder if someone could help clarify waveguiding with broadband, incoherent light please.</p>
<p>If we take a telecomms fiber, which is single-moded above ~1.4 μm and couple a laser beam in, we assume this excites the only mode, which is the fundamental mode. The mode-field diameter of the transverse mode is dete... | 6,154 |
<p>I want to learn physics and the math required, but I never got the chance to learn properly in school due to mental illness. But, now, as a 22 year old, I wish I can start learning. Attending a college is not an option as I do not think I would find one that is willing to provide the psychological support a person s... | 98 |
<p>How to prove that $\ln(Z(J))$ generates only<a href="http://en.wikipedia.org/wiki/Feynman_diagram#Connected_diagrams%3a_linked-cluster_theorem" rel="nofollow"> connected Feynman diagrams</a>? I can't find the proof of this statement, and have only met its demonstrations for case of 2- and 4-point.</p> | 6,155 |
<p>It is known that 3D Chern-Simons(C-S) theory has no explicit metric involving in the Lagrangian density: </p>
<p>$$
A \wedge dA + (2/3) A \wedge A \wedge A
$$</p>
<p>while the 4D Yang-Mills(Y-M) theory has the metric $g_{\mu\nu}$involves.</p>
<p>$$
F \wedge *F= (dA + A \wedge A) \wedge *(dA + A \wedge A)
$$
More ... | 6,156 |
<p>If I'm in Chile, Santiago, what is the best time of the year to see the star <a href="http://en.wikipedia.org/wiki/Alpha_Centauri" rel="nofollow">Alpha Centauri</a> at the beginning of the night? </p> | 6,157 |
<p>120 volts x 20 amps = 2,400 Watts </p>
<p>However, if I increased the voltage and lowered the current, you can also use a smaller wire size (more inexpensive), also have less heat and achieve the same watt Power.</p>
<p>1,000 volts x 2.4 amps = 2,400 Watts</p>
<ol>
<li>Why doesn't it heat up like current?</li>
<l... | 6,158 |
<p>Now that scientists found the primordial gravitational waves that formed shortly after the big bang,and we all now that just after the bang the 4 fundamental forces were unified can we consider that these waves are the strings that we're looking for,that unify again these forces?</p> | 6,159 |
<p>Is there a simple method of determining, given a UTC date/time, whether it is day or night at a given lat/long coordinate?</p>
<p>I am currently using a formula based on a <a href="http://williams.best.vwh.net/sunrise_sunset_algorithm.htm" rel="nofollow">Sunrise/Sunset Algorithm from the US Naval Observatory</a>, b... | 6,160 |
<p>I'm at about 40deg north so, assuming a clear southern horizon, I can't see things below about -30 or so (I actually don't know how far south). I also have a large portion that is circumpolar so it's always visible. I assume there's an equal size area south that is never visible.</p>
<p>On an equinox, the average... | 6,161 |
<p>I would like to have some examples of classical systems with "strong" coupling coefficient (in their action term). Specifically, I am looking for intermediate or cross-over ranges of coupling (~$\mathcal O(1) $), where it is neither possible to describe them by effective (composite) field theories with small couplin... | 6,162 |
<ol>
<li><p>Is it me who have a poor understanding, or does all matter have to become 'pure energy' in order to achieve speed-of-light speed? </p></li>
<li><p>If so, does that mean that no material can achieve the speed of light and remain in its original state of matter?</p></li>
</ol> | 6,163 |
<p>Is there any realistic, understandable, provable (even in some extent) explanation/model for the extent of the universe?
What is its shape? and Why? I mean physical explanations not philosophical since the question is about a physical entity, the universe.
When I try to think about this it is almost I cannot think a... | 6,164 |
<p>When you place a water or food in a microwave oven, it heats.
Which process commits more energy to that: <a href="http://en.wikipedia.org/wiki/Dielectric_heating">dielectric heating</a>, or ion drag i.e. <a href="http://en.wikipedia.org/wiki/Joule_heating">resistive heating</a>?</p>
<p>AFAIK, in distilled water (wh... | 6,165 |
<p>In what relation is the energy input in an alternating current circuit to its frequency?</p>
<p>I'd guess I have to compute something like</p>
<p>$$E=\int P(\omega,t) dt=\int U(\omega,t) I(\omega,t) dt, $$</p>
<p>but if say </p>
<p>$$U(\omega,t)\propto\sin{(\omega t)},$$</p>
<p>then it seems part of the integra... | 6,166 |
<p>Who first determined the structure of water (two hydrogen atoms stuck to an oxygen atom at approx 105 degrees), and, more importantly, how was this done? </p> | 6,167 |
<p>Recently in our area there has been a large forest fire and I've been looking into home defense from such things.</p>
<p>I am not a physicist - but can do some basic math.</p>
<p>I was wondering how I could calculate if a 'evaporative mister' type system could be used for such to reduce the ambient air temp to sto... | 6,168 |
<p>There are multiple theories about time traveling. One is "proven": The time slows down according to your speed. The satellites in space are traveling faster than us, thus their clocks slows down a bit. So by traveling at the speed of light, you would travel without the time. So the time stops when you are traveling ... | 6,169 |
<p>An astronaut camps on the moon for a period of one month as per the earth’s calendar.
What would be the path of the earth seen by the astronaut in the lunar sky?</p>
<p>(A) The earth remains approximately at a fixed altitude and direction.</p>
<p>(B) The earth completes one revolution parallel to the lunar horizon... | 6,170 |
<p>I want a different proof of 6 degrees of freedom of a solid object made of $\ N$ particles. I am thinking along these lines:</p>
<p>Definition of rigid body is</p>
<p>$\ modulus[\vec{r_i}-\vec{r_j}]=constant \ \forall\ i,j$</p>
<p>This gives me $\ ^NC_2$ constraints. There exist in total $\ 3N$ equations. So the ... | 6,171 |
<p>Is this proof of spin-statistics theorem correct?</p>
<p><a href="http://bolvan.ph.utexas.edu/~vadim/classes/2008f.homeworks/spinstat.pdf" rel="nofollow">http://bolvan.ph.utexas.edu/~vadim/classes/2008f.homeworks/spinstat.pdf</a></p>
<p>This proof is probably a simplified version of Weinberg's proof.
What is the ... | 767 |
<p>For example, the radiation dominated cosmology, the energy density of radiation is propotional to $a^{-4}$ and
the volume is propotional to $a^3$, where $a$ is the scale factor. So the total energy of radiation is propotional to $a^{-1}$. So where is the loss of energy of radiation? Is the gravitational field has t... | 6,172 |
<ol>
<li><p>What is the mass of a photon moving at the speed of light? </p></li>
<li><p>And if it does not have mass, how is it affected by gravity?</p></li>
<li><p>Also why does Einstein's general relativity support that a gravitational wave must travel at the speed of light?</p></li>
</ol>
<p>I'm just an A-level stu... | 195 |
<p>I've been exploring techniques in statistical physics, specifically applying them to spin ices. I'm in the canonical ensemble. By using the fluctuation dissipation theorem you can extract useful properties from the variance in energy and magnetization such as the heat capacity (constant V) and magnetic susceptibilit... | 6,173 |
<p>I'm writing a novel and I'm quite confused if this system could be possible in the real universe. Is it possible that a system exist, where 5 identical planets which could be of same characteristics (Inclination, speed, planetary mass and others) revolve around a single star. Also, What effects would the 5 planets u... | 6,174 |
<p>I am answering some exercises in thermodynamics, and I am still in trouble with some values and constants.
In the exercise, it is given: $\mu_\text{air}=1.8\cdot10^{-5}~\text{kg/m s}$. What for is this value used? In the case, I need to find some tensions in given points, and I know the speed profile of the air.</p>... | 6,175 |
<p>I have two masses connected by a spring. They are horizontal and are not affected by friction or gravity.</p>
<p><img src="http://i.stack.imgur.com/S34Hs.png" alt="Mass Spring System"></p>
<p>The spring's stiffness constant is $k$, and $x_1$ and $x_2$ are the displacements of the masses from their equilibrium pos... | 216 |
<p>This is a sequel to <a href="http://physics.stackexchange.com/q/24188/2451">this</a> question.</p>
<p>Who knows a difference between the Lagrangian in <a href="http://en.wikipedia.org/wiki/Special_relativity" rel="nofollow">SR</a> and <a href="http://en.wikipedia.org/wiki/General_relativity" rel="nofollow">GR</a> f... | 6,176 |
<p>This is what my textbook says about the Michelson-Morley experiment:</p>
<p>"This invariance of the speed of light between inertial reference frames means that there must be some relativity principle that applies to electromagnetism as well as to mechanics. That principle cannot be Newtonian relativity, which impli... | 6,177 |
<p>All of the sources I have found for this online have been wildly unclear. Many use the phrase "Fermi energy" to refer to the "Fermi <em>level</em>" (which is emphatically <em>not</em> what I'm looking for; I want the Fermi energy as defined in this Wikipedia article: <a href="http://en.wikipedia.org/wiki/Fermi_energ... | 6,178 |
<p>is such a <em>tensor</em>, $T_{\alpha\beta\, \gamma}$, possible such that
$$T_{\alpha\beta\, \gamma}=T_{\beta\alpha\, \gamma}=-T_{\alpha\gamma\, \beta}=-T_{\gamma\beta\, \alpha}$$
That is, symmetric under two indices, but antisymmetric under the third with the previous too. If so can it be build up by a linear comb... | 6,179 |
<p><img src="http://i.stack.imgur.com/twSPw.jpg" alt="enter image description here"></p>
<p>For part (a), is the normal force by the hinge on the bridge at an angle or is it horizontal?</p>
<p>For part (b), I know how to resolve forces horizontally and vertically, and to take torques about the hinge, but the informat... | 6,180 |
<p>In Green-Schwarz-Witten Volume 2, chapter 15, it is argued (roughly) that we need 6-dimensional manifolds of $SU(3)$ holonomy in order to receive 1 covariantly constant spinor field. And it turns out that <a href="http://en.wikipedia.org/wiki/Calabi%E2%80%93Yau_manifold" rel="nofollow">Calabi Yau manifolds</a> sati... | 6,181 |
<p>By an ideal conductor, I mean one with zero resistance. Inside an ideal conductor with no current, the electric field is zero, but is the electric field still zero with the ideal conductor carrying a current?</p> | 6,182 |
<p>You are given a long length W of copper wire. How would you arrange it to obtain the maximum self-inductance? Why?</p>
<p>I am trying to use the equation</p>
<p>$$L=\mu_o n^2 l A$$</p>
<p>I try to solve it using a fixed length wire of 10 units, width 1mm and winding it into a solenoid. I plug in values of circu... | 6,183 |
<p>We have a simple circuit given, a resistor $R_x$ and a fixed current source with $I = 50 \, \mathrm{\mu A}$. Now over the resistor there is a currentmeter which has an internal resistance. In any case some of the current will go through the currentmeter and therefore the result will be slightly off.</p>
<p>The ques... | 6,184 |
<p>I'm trying to understand the Blasius boundary layer solution, but I'm having some difficulties. Using wikipedia, I wonder how they get the first formula: <a href="http://en.wikipedia.org/wiki/Blasius_boundary_layer" rel="nofollow">http://en.wikipedia.org/wiki/Blasius_boundary_layer</a>. $$\frac{U^2}{L}\approx\nu \fr... | 6,185 |
<p>It's usually said that black umbrellas are best against sun, since black absorbs most of the radiation . The common umbrellas in market(atleast in India) are painted black outside and silvery inside. </p>
<p>However I think the reverse(silvery outside, black inside) should be more effective. The outer color(silvery... | 6,186 |
<p>I am confused with physical picture about unpolarized light.</p>
<p>Is unpolarized light very fast rotating polarized light? or co-existing state of two orthogonal polarization? (or something else?)</p>
<p>If there is a linear polarizer which rotates very very fast and randomly (the polarizer in imagine), the outp... | 6,187 |
<p>How will act low pressure container, or what would happen inside the low pressure container when it is placed inside the container with high pressure?</p>
<p>And if it is high pressure container inside the high pressure container?
Will the container which is inside stay in the centre?</p> | 6,188 |
<p>In high school we are taught that magnetic field perpendicular to velocity of an charged particle experience perpendicular force that causes it to move in circular path by relation
$$qvB=\frac{mv^2}{r}$$ but in drawbacks of Bohr's theory it was proposed that accelerated charged electron orbiting along nucleus will i... | 6,189 |
<p>we are doing K space calculation(transnational invariant basis) of Hamiltonian, and trying to compare with exact method for same nos of sites and particles, we are getting big difference in ground state energy. Is it coming because of Hamiltonian is complex in K-space calculation and real in exact calculations.I am ... | 6,190 |
<ul>
<li><p>Broadly I would like to understand what is the difference in the physical interpretation of a (Euclideanized) QFT which is on space-time $S^d$ and which is on a space-time $S^{d-1}\times S^1$. </p>
<p>In the later case I am comfortable thinking of it as being a theory actually on a Lorentzian space-time w... | 6,191 |
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