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<p>The inspiration for this question is <a href="http://cooking.stackexchange.com/questions/17529/surface-tension-in-food">over on cooking.stackexchange</a>, asking more about actual measurements for commonly consumed liquids, but I'm interested more generally as well.</p>
<p>What determines the behavior of surface te... | 6,280 |
<p>The neutron decay is a spontaneous process. After isolating neutrons the mean lifetime is approx. 15 minutes. The real moment when the neutron decays is not affected by us. That's why, it is allowed to speak about <a href="https://en.wikipedia.org/wiki/Hidden_variable_theory" rel="nofollow">hidden parameters</a>?</p... | 6,281 |
<p>What is the difference between $\tau_{xy}$ and $\tau_{zy}$; because as far as i know the first character of subscript represents the direction to which the stress is perpendicular and other the actual direction.</p>
<p>So a vector perpendicular to $x$ along $y$ and another perpendicular to $z$ along $y$, shouldn't ... | 6,282 |
<p>Consider the product of two left Weyl spinors in the notation commonly found in supersymmetry,
\begin{equation}
\chi ^\alpha\eta_\alpha = \chi ^\alpha \epsilon _{ \alpha \beta } \eta ^\beta
\end{equation}
This is equal to,
\begin{equation}
\left( \begin{array}{c}
\chi ^\alpha \\
0
\end{array} \right) ^T\l... | 6,283 |
<p>I am trying to find out the <a href="http://en.wikipedia.org/wiki/Uninterruptible_power_supply" rel="nofollow">UPS</a> capacity in amp-hours for my HP UPS system.
I've already done some calculations based on the UPS information from the HP Power Manager software.</p>
<p><img src="http://i.stack.imgur.com/rdvd0.png"... | 6,284 |
<p>The hydrogen atom contains 1 proton and 1 electron. The radius of the proton is approximately 1.0 fm (femtometers), and the radius of the hydrogen atom is approximately 53 pm (picometers).</p> | 6,285 |
<p>For an electron in its rest frame, we have an entropy
$$
S = \log 2,
$$
which comes from the 2 possible spin directions along z-axis. </p>
<p>If the measurement $S_z$ changes its state to $\left| + \right>$, the entropy goes to zero.</p>
<p>Does this violate the second law of thermodynamics?</p> | 6,286 |
<p>Pioneer space probe moving at a speed of $30km/s$.
Assuming its heading for Proxima Centauri, which is situated at $4.2ly$ from earth, calculate how long it would take to get there in years, to the nearest year?</p>
<p>Could you please help.</p> | 6,287 |
<p><img src="http://i.stack.imgur.com/MbcF9.gif" alt="enter image description here"></p>
<p>This is my opinion about what we will see. When the pipe arrive at the bar, we will be unable to see some part of it anymore (the pipe will absorb the light emitted by the bar), even if the pipe and the bar didn't appear to us ... | 6,288 |
<p>This question is coming from someone who has very little experience with M-Theory but is intrigued by the AdS/CFT correspondence and is beginning to study it.</p>
<p>Why is the gauge/gravity duality discussed almost always in the context of anti-deSitter space? What is unique about it? What are the difficulties in ... | 6,289 |
<p>I was recently watching a show that say we need at least 5 Higgs Boson to prove the existence of the dark matter because it will strengthen the concept of symmetry.</p>
<p>Why is that so? Because, I am not getting what it says.</p> | 6,290 |
<p>What is the Noether charge associated with Kahler invariance of <a href="http://en.wikipedia.org/wiki/Supergravity" rel="nofollow">supergravity</a> (SUGRA)? As the question is rather tangential to what I need to do, I have not tried explicitly calculating it myself, but I'm sure that I'm not the first one to wonder.... | 6,291 |
<p>Suppose I want to know what the universe looks like from the perspective of a frame of reference moving at $c$ relative to my current frame. As discussed at length in various other questions on this forum, from the perspective of the current established theory of special relativity, the notion of such a frame is mor... | 6,292 |
<p>This question is an outgrowth of <a href="http://physics.stackexchange.com/questions/15402/regarding-voltage-and-emf">regarding voltage and emf</a> where @sb1 mentioned Faraday's law. However, Faraday's law as part of Maxwell's equations cannot account for the voltage measured between the rim and the axis of a Farad... | 6,293 |
<p>Electron as an example has a de Broglie wavelength and could diffract.
If it has a single wavelength the time extent of the particle's pulse duration would be infinite ..
If it carries a broadband will be finite in time .. my question is how is it determined the duration in time of the electron or it is assumed to ... | 6,294 |
<p>Just a quick check: If given a time-independent wavefunction of the form $$\psi(x) = e^{ikx}f(x)$$, where $f(x)$ any arbitrary function of $x$ but one can't factor out another $e^{i\alpha x}$, $\alpha\in\mathbb R$.</p>
<p>Could I then immediately conclude that $k^2= \frac{2mE}{\hbar^2}$? Is there a name for this qu... | 6,295 |
<p>Experimentally, I have seen how hooking up a battery to a simple circuit just with a high-resistance voltmeter raises the voltage reading (allegedly to a level equal to the EMF of the battery).</p>
<p>However, I find the explanation for why the reading rises, much less to an EMF, very unconvincing. We were told th... | 6,296 |
<p>We always assume that all the voltage, in no matter what type of (basic, I guess) circuit we are dealing with, is used up. I can see why this is true. Imagine a circuit with low resistance - and correct me if I am wrong, but from electrostatics, we know that an electric field, similar to magnetic fields, accelerates... | 6,297 |
<p>Suppose a man falls into very cold water and gets their foot stuck under a heavy rock. Fortunately, his head is above water and someone is able to call for help. The paramedics want to keep him warm while they work on freeing his foot. They put a hat on his head. Should they also wrap him in a blanket?</p> | 6,298 |
<p>Where can a good treatment of the <a href="http://en.wikipedia.org/wiki/Adiabatic_theorem#Diabatic_passage" rel="nofollow">'sudden' perturbation approximation</a> be found?</p>
<p>A lot of quantum mechanics books have very brief discussions of it but I want to see it in some detail and preferably with as many examp... | 6,299 |
<p>I'll try to be clear: example: If you send the ISS far enough for it not to undergo the Earth's gravity anymore, then you turn it and the—sleeping—astronauts in it upside down, when they wake up, will they know/feel that they're not the right way up? How?</p> | 6,300 |
<p>How can one show that $\int_{-\infty}^{\infty}\psi^*(x)(d/dx+\tanh x)(-d/dx+\tanh x)\psi(x) dx=\int_{-\infty}^{\infty} |(d/dx+\tanh x)\psi(x)|^2 dx$, where $\psi$ is normalized? </p> | 6,301 |
<p>I know that parallel light beams hitting a parabola will be focused at the focus of the parabola (<code>f = 1/4a</code>) and a light source at the focus of the parabola will produce parallel light. What will happen if the light was not parallel but came from a light source shorter then the focus of the parabola and ... | 6,302 |
<p>A classic example for the method of images is the following, quoted from Griffiths's Introduction to Electrodynamics, page 121:</p>
<p>"Suppose a point charge $q$ is held a distance $d$ above an infinite grounded conducting plane. Question: What is the potential in the region above the plane?" </p>
<p>Griffiths co... | 6,303 |
<p>Consider two stationary charges, one positive the other negative. Their potential energy is clearly negative. So you would expect that the energy density of the associated electric field would also be negative. But it isn’t. It’s the square of the electric field and therefore positive. Why isn’t the energy dens... | 6,304 |
<p>Reading an interesting article on a recent ArXiv paper by Carlo Rovelli and Francesca Vidotto on so-called Planck stars, at</p>
<p><a href="https://medium.com/the-physics-arxiv-blog/6cf7ec0ed28b" rel="nofollow">https://medium.com/the-physics-arxiv-blog/6cf7ec0ed28b</a></p>
<p>I was struck by the observation that t... | 220 |
<p>I understand the mechanism how <a href="http://en.wikipedia.org/wiki/CHSH_inequality" rel="nofollow">CHSH Inequality</a> works. One thing bugs me is why $\pi/8$. </p>
<p>I can also take $\pi/100$ for example and $\cos^2(\pi/100)> \cos^2(\pi/8)$ so much better probability and it doesn't contradict with the explan... | 6,305 |
<p>Does reactive force require the two force involved have to have two medium for reactive force to occur?</p>
<p>I know the fuel-thruster is working on vacuum space, but we human could not use arm to swim in space?</p>
<p>For example, two baseball hitting together have two medium</p> | 6,306 |
<p>I have some confusion between with resolving the following situation.</p>
<p>I know that no measurable quantity can have a value of infinity. For example, I just wrote something out, but clearly this doesn't work, since infinity is not really a number and thus measurable entities can't be quantified as being of inf... | 6,307 |
<p>I have a <a href="http://en.wikipedia.org/wiki/Hammock" rel="nofollow">hammock</a> that I want to hang using a tree on one end and a wooden post set in a bucket of cement on the other end.</p>
<p>How would I determine how heavy the cement needs to be so that it would support the weight of a 250lbs person in the ham... | 6,308 |
<p>We have the famous equation $E = mc^2$, and we also believe that matter is made of particles.</p>
<p>Then, What is the energy made of? If the two are interchangeable, there must be some common building block to both for sure. Isn't it?</p>
<p>If energy is made of "Nothing", how could it be converted to matter?</p> | 6,309 |
<p>I am reviewing some old material I learned years ago and am having trouble figuring this one out. Can somebody confirm that I have done my math correctly, and tell me how I can recover the field of view from these parameters?</p>
<p>I have a $3.6$(height) by $4.8$(width) mm sensor, which displays as $640\ by\ 480$... | 6,310 |
<p>Yesterday I asked whether the Schroedinger Equation could possibly be nonlinear, after reviewing the answers and material given to me in that thread I feel like my question were adequately answered.</p>
<p>However could there still be nonlinear dynamics underneath quantum mechanics that could potentially explain th... | 6,311 |
<p>I can't solve a problem:</p>
<p>$ A= 0.5 (ms)^{-1}$, $ x_0 = 0.5 m $, $v(t)= A \cdot x^2 $, I have to compute the position at $t=3$ ($x_0$ is the initial position). </p>
<p>So my guess is that I should be able to compute the $x(t)$ formula by integrating $v(t)$: </p>
<p>$$ \int^t_0 A \cdot x^2 dt = x_0 + A \cdo... | 6,312 |
<p>The sun pulls on the moon with a force that is more than twice the magnitude of the force with which the earth attracts the moon. Why, then, doesn’t the sun take the moon away from the earth?</p> | 6,313 |
<p>How can I see, using group theoretic arguments, that a the quantum of a gravitational wave has spin 2? </p>
<p>How can one show that it is described by a 5 dimensional representation of $SO(3)$?</p>
<p>I know the argument from Carroll's book on General Relativity: from looking at the perturbation on the geodesics ... | 6,314 |
<p>I have derived the energy conservation equation:</p>
<p>\begin{equation}
\frac{\partial}{\partial t} \left [ \frac{1}{2} \rho v^2 + \varepsilon + \rho \phi \right ] + \frac{\partial}{\partial x_j} \left [ \frac{1}{2} \rho v^2 v_j + \rho h v_j + \rho \phi v_j \right ]=0
\end{equation}</p>
<p>where $\varepsilon$ is ... | 6,315 |
<p>We have 2 EPR experiments running in parallel, with Alice having one leg of each (a1,a2) and Bob the other leg of each (b1,b2). Thus (a1,b1) are anticorrelated, as are (a2,b2). Thus also (a1,a2) are uncorrelated as are (b1,b2). Now Alice locally entangles (a1,a2), and Bob measures b1 and b2. After repeating the enti... | 6,316 |
<p>I'm reading the section on scattering in Goldstein's Classical Mechanics, and I have a rather basic question about this. </p>
<p>It says that scattering in the laboratory is a two-body problem because of the recoil of the scatterer. Therefore, we convert the obtained data into center of mass coordinates in order to... | 6,317 |
<p>Why is the magnetic flux not quantized in a standard <a href="http://en.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect" rel="nofollow">Aharonov-Bohm</a> (infinite) solenoid setup, whereas in a superconductor setting, flux is quantized?</p> | 6,318 |
<p>I have started reading the book Connectivity and Superconductivity which gives an introduction to the ideas of de Gennes-Alexander theory. My question is: how is this theory regarded experimentally? Besides the sophisticated math approach,does it give good experimental results?</p> | 6,319 |
<p>[<b>Update:</b> Thanks, everyone, for the wonderful replies! I learned something extremely interesting and relevant (namely, the basic way decoherence works in QFT), even though it wasn't what I thought I wanted to know when I asked the question. Partly inspired by wolfgang's answer below, I just <a href="http://p... | 6,320 |
<p>The kinetic energy of a particle is a periodic function in time. Does it imply that the particle is in a conservative force field and there are no dissipative forces acting on it at any instance of time ?</p>
<p><strong>EDIT</strong> (in view of comment by Willie)</p>
<p>Please consider the question as "Is the for... | 6,321 |
<p><img src="http://i.stack.imgur.com/L5thM.png" alt="enter image description here"></p>
<p>The image above shows the distribution of the surface charge in a current carrying wire. The surface charges distributes themselves to make sure the field inside the wire is always perpendicular to the surface of the wire. </p>... | 6,322 |
<p>COG: The lower the center of gravity, the more stable and object is.
Rotational Inertia: The farther the concentration of mass from the defined axis of rotation, the more resistance the object has to movement.</p>
<p>I'm quite confused between these two statements. </p> | 6,323 |
<p>I have read before in one of Seiberg's articles something like, that gauge symmetry is not a symmetry but a redundancy in our description, by introducing fake degrees of freedom to facilitate calculations.</p>
<p>Regarding this I have a few questions:</p>
<ol>
<li>Why is it called a symmetry if it is not a symmetr... | 6,324 |
<p>So, the quantum path integral is a generalization of the classical principle of least action- but here we know that all paths contribute something finite to the probability density. What confuses me is that this doesn't seem to involve the quantization of energy (action) at all. How does this come into play? Is it a... | 6,325 |
<p>I have a question in Srednicki's QFT textbook.
In order to compute the vacuum to vacuum transition amplitude given by :
$$\left \langle 0|0 \right \rangle_{J}~=~\int \left [ d\varphi \right ]e^{i\int dt ~L\left ( \varphi ,\partial _{\mu }\varphi \right )},$$</p>
<p>one has to Fourier transform the field to the mo... | 6,326 |
<p>I have been reading the stackexchange questions on enhanced symmetries in string theory, the Leech lattice, monstrous moonshine, etc. , and I have a question to ask.</p>
<p>An astute commentator pointed out with enhanced symmetries, massless vector bosons have to couple in the Yang-Mills fashion. Only if the massle... | 6,327 |
<p>See the pictures below. A pair of sunglasses I recently purchased has the polarization axis in one lens offset about 20 degrees (by eyeball estimation) from the other. I don't have much experience with other polarized sunglasses, but this seems very obviously wrong to me. And it's very noticeable while wearing th... | 6,328 |
<p>The mass of an elementary particle in string theory is related with the way the string vibrates. The more frantically a string vibrates the more energy it posses and hence the more massive it is. My question is how is the electric charge of a particle is described in S.T. How is the opposite charges described? More ... | 6,329 |
<p>I'd like to make a comparison of prices, availability and properties of semiconductor substrate layers like Si, Ge, GaP, AlN etc. I wonder what are the problems related to getting such data, what are the leading companies that sell such things, what's the quality, waiting time and so on. I'm not going to buy one, It... | 6,330 |
<p>I thought that it was valid for very low temperatures since for it to be valid I think that it is necessary to be in the non-degeneracy condition, which requires $E_G >> k_B T$ (with $E_G$ being the energy gap), that it is satisfied at very low temperatures... But maybe at too low temperatures the non-degenera... | 6,331 |
<p>I've just finished a Classical Mechanics course, and looking back on it some things are not quite clear. In the first half we covered the Lagrangian formalism, which I thought was pretty cool. I specially appreciated the freedom you have when choosing coordinates, and the fact that you can basically ignore constrain... | 6,332 |
<p>I'm not a physicist but I'm interested in <a href="http://en.wikipedia.org/wiki/Theory_of_everything" rel="nofollow">unified theories</a>, and I do not know how to start learning about it. What would be a good book to read to start learning about this topic?</p> | 726 |
<p>If I had a piece of metal and i wanted it to be negatively charged.
How can I do that?</p> | 835 |
<p>Is it true that all static solutions in GR are also spherically symmetric? Is there a proof of this?</p>
<p>Similarly, are all stationary solutions axisymmetric? </p> | 6,333 |
<p>i have an incident plane wave and a dipole, consider that plane wave incident on dipole. at this moment what happen for dipole ? we know that after incident of plane wave on dipole, the radiation have occurred, and i want derive the <strong>phase difference between radiation field and incident plane wave field</stro... | 6,334 |
<p>Why Magnifying glass(convex lens) produces heat when placed in front of sun? </p> | 6,335 |
<p>The problem asks me to find the density of gas in a cylinder of radius $R$ and length $l$ rotating about its axis with angular velocity $ω$, there being a total of $N$ molecules in the cylinder.</p>
<p>What I have done is shown as following:</p>
<p>I choose to look this scenario in a static frame with the cylinder... | 6,336 |
<p>Let's say you have a traffic light with the well known red, yellow, and green tinted glasses. </p>
<ul>
<li>Setup 1: Each glass has a white light bulb behind it.</li>
<li>Setup 2: Each glass has a colored bulb behind it which matches the tint on the glass. So there is a red light behind the red glass, a yellow ligh... | 6,337 |
<p>I understand that a reversible computer does not dissipate heat through the Landauer's principle whilst running - the memory state at all times is a bijective function of the state at any other time.</p>
<p>However, I have been thinking about what happens when a reversible computer <em>initializes</em>. Consider th... | 6,338 |
<p>Without reducing the energy more than necessary due to the frequency decrease? And if this happens/works, is there an index of such materials and their optic properties?</p> | 6,339 |
<p>The uncertainty principle says that the product of the uncertainties in position and momentum can be no smaller than a simple fraction of Planck's constant $h$. </p>
<p>Several articles lately suggest this is not true.</p>
<p>Today in <a href="http://physicsworld.com/cws/article/news/2013/nov/01/uncertainty-reigns... | 6,340 |
<p>The fundamental question is</p>
<blockquote>
<p>Why is Hall conductance quantized?</p>
</blockquote>
<p>Let's start with the Hall bar, a 2D metal bar subject to a strong perpendicular magnetic field $B_0$. Let current $I$ flow in the x-direction, then the y-direction develops a voltage $V_H$. The Hall conductanc... | 6,341 |
<p>I know Fermi's Golden Rule in the form</p>
<p>$$\Gamma_{fi} ~=~ \sum_{f}\frac{2\pi}{\hbar}\delta (E_f - E_i)|M_{fi}|^2$$</p>
<p>where $\Gamma_{fi}$ is the probability transition rate, $M_{fi}$ are the transition matrix elements.</p>
<p>I'm struggling to do a derivation based on the density of states. I know that ... | 6,342 |
<p>I've been discovering recently the concept of noise spectrum, defined as:
$$S_{xx}[\omega] = \int dt<x(t)x(0)>\text{e}^{-i\omega t}$$
Roughly the Fourrier transform of the two-point function.
Apparently it represents, the probability that the system has to absorb (or emit) energy for positive (negative) $\omeg... | 6,343 |
<p>I have read that we can charge a capacitor using a battery, but can the vice versa happen? My project needs to show a battery being charged through a fully charged capacitor.</p> | 6,344 |
<p>I recently used an oscilloscope in X-Y mode to draw the phase ellipsis of two voltages. I then used the formula phi = arcsin(2y/B) where y is the value of the ellipsis at x = 0 and B is the total distance from the highest point of the ellipsis to the lowest.</p>
<p>Now I really want to know why this works, thank yo... | 6,345 |
<p>Are tidal power plants slowing down Earth's rotation to the speed of the orbiting moon? (1 rotation per 28 cca days) </p>
<p>Are they vice versa increasing the speed of moon orbiting by generating some waves in gravitation field?</p>
<p>If yes, can you calculate how much energy must be produced by how many tidal p... | 349 |
<p>When the focal length of a camera gets further, the object projected on the image gets larger. But would more or less of the object be projected on the image?</p>
<p>I know the answer is that less of the object would get projected on the image because just try it on a camera and I could see the effect. But I don't ... | 6,346 |
<p>The phrase "speed of light" is commonly used for the constant c =3E8 m/s, a feature that's "hardcoded" into the structure of spacetime. All massless waves and particles move at this speed, and it's a key concept in all fundamental theories in physics.</p>
<p>Light, in vacuum, is one fine example. But light in air... | 6,347 |
<p>I have this question related to the the Noether's Theorems.
I want to know a rigorous enough enunciation of this theorem, the context is Classical Field Theory without fancy geometrical structures but the usual stuff you need to know to do QFT and the use of Lie Groups(without being too abstract, I need a sensible ... | 6,348 |
<p>We don't get eigenstates of momentum when we operate momentum operator in the wave function of particle in a 1D box problem yet we say momentum is quantized in this situation. Why is it so?</p> | 6,349 |
<p>Could we still use Newtonian mechanics in a frictionless world?</p> | 6,350 |
<p>I remember reading about all chicken at a poultry farm being violently sick/dying for apparently no reason. It turned out the culprit was machinery at a nearby factory that emitted sound at a frequency equivalent to the resonant frequency for brain cavity of the chicken. </p>
<ul>
<li>Could the story be true?</li>
... | 6,351 |
<p>What is the period of the pattern from the double slit experiment? It varies along the pattern right?
Namely I'm confused because when considering two point sources (See:
<a href="http://physics.stackexchange.com/questions/87287/period-of-interference-pattern-on-a-substrate">Period of Interference Pattern on a Subs... | 6,352 |
<p>I understand how mathematically is possible to have one object with elliptical or circular orbit around another object in space.</p>
<p>so can I think of it as a limit cycle? If yes, then is it stable or unstable? and why?</p>
<p>The intuition behind my question is to know if due to friction we will have a Moon-Ea... | 221 |
<p>Why the ratio of a circle's circumference to its diameter is always the constant $\pi$?
Moreover many of you know better than me about <em>golden ratio</em> $\phi$, <em>Euler's number e,</em> and many other constants. How explain this while everything seems to be in chaos? Is there any explanation for this kind of q... | 6,353 |
<p>In a nozzle, the exit velocity increases as per continuity equation $Av=const$
as given by Bernoulli equation (incompressible fluid). Pressure is inversely proportional to velocity, so we have lower pressure at the exit of the nozzle. But as per definition of pressure, $P=F/A$, i.e., pressure is inversely proportion... | 6,354 |
<p>It appears that in Japan, there is an old custom called Uchimizu. The name is a combination of words "road" and "water". The essence of it is moisturizing small parts of populated areas like sidewalks, streets, parks, gardens. A very nice diagram explaining how Uchimizu is performed can be found on <a href="http://w... | 6,355 |
<p>With degrees in Mechanical and Electrical engineering but no advanced education in physics, I submit a query based on ellipsometric macro photography of TEMS supplied by FDA/NIH. In one TEM a triangle of RNA/DNA indicates ionic activity.<br>
PHOTO 1. <img src="http://i.stack.imgur.com/mMdGD.jpg" alt="100nm RNA/DNA... | 6,356 |
<p>When discussing the Schroedinger equation in spherical coordinates, it is standard practice in QM handbooks to point out that the radial part of the 3-dimensional wave equation bears a strong analogy to the corresponding 1-dimensional case. This is because the Laplace operator in spherical coordinates can be written... | 6,357 |
<p>So there has been talk in the news of a star named Methuselah that is <a href="http://www.space.com/20112-oldest-known-star-universe.html" rel="nofollow">"older than the universe"</a>. Moreover, this star happens to belong to our very own Milky Way. </p>
<p>The article mentions that Methuselah is consistent with un... | 6,358 |
<p><img src="http://i.stack.imgur.com/Hgytn.jpg" alt="enter image description here"></p>
<p>This picture violates some laws of physics. Am I right?</p> | 6,359 |
<p>Is an excited atom more likely to emit a photon if there is a similar atom in the ground state nearby ready to absorb it?</p>
<p>When I say "nearby" I guess I mean that the absorber has an approximately zero <strong>spacetime</strong> separation from the excited atom.</p>
<p>I suppose there are a vast number of gr... | 6,360 |
<p>In quantum field theory, we are looking for a Lagrangian that is, amongst other, renormalizable. But how do we determine whether or not a theory is renormalizable? Is this purely done by power counting due to Weinberg? <strong>This question is already answered in the a <a href="http://physics.stackexchange.com/quest... | 6,361 |
<p>While trying to actually understand the difference between <a href="http://en.wikipedia.org/wiki/Quantum_nondemolition_measurement#Description_from_the_literature" rel="nofollow">QND</a> and <a href="http://en.wikipedia.org/wiki/Complete_set_of_commuting_observables" rel="nofollow">CSCO</a>, I went and found the rel... | 6,362 |
<p>I've often seen the Casimir effect cited as a source of negative energy/exotic matter with regards to ideas like the Alcubierre drive. The articles then go on to note that the energy required by the Alcubierre drive is orders of magnitude more than that produced in theory by the Casimir effect.</p>
<p>Fair enough. ... | 6,363 |
<p>How can I determine the needed initial velocity to make a 2d wind resistance free projectile (in computer simulation) reach maximum height at a certain x distance away, with launch position and target position on uneven ground?</p> | 6,364 |
<p>If I have a projectile shot in a vacuum-box that has no gravity or wind resistance inside it (lets say the box is 1000 units tall and 1000 units wide), with the only rule being that the projectile bounces off the sides of the box how do I solve for the angles that will hit any target inside the box from a projectile... | 6,365 |
<p>I just came from a class on Fourier Transformations as applied to signal processing and sound. It all seems pretty abstract to me, so I was wondering if there were any physical systems that would behave like a Fourier transformation.</p>
<p>That is, if given a wave, a purely physical process that would "return" th... | 6,366 |
<p>When cooking pasta, some organic foam usually forms on the surface of the boiling water and the situation can be kept under control by adjusting the heat (and/or adding some oil).
Covering the pot with a lid, even loosely so, usually leads to the foam overflowing within a short time (removing the lid fixes the probl... | 6,367 |
<p>One of the experimental evidence that supports the theory of big bang is cosmic microwave background radiation (CMBR). From what I've read is that CMBR is the left over radiation from an early stage of the universe.</p>
<p>My questions are: </p>
<ol>
<li><p>Why are we able to detect this radiation at all? </p></l... | 6,368 |
<p>I have spent an unreasonable amount of time trying to plot $F(r,\theta,\phi)$ plane slices in MATLAB. I want to look at $x-y,y-z,x-z$ planes. Here's the function, specifically:</p>
<p>$$F(\rho,\theta,\phi)~=~4\pi\rho^{2}|\frac{\rho e^{\frac{-\rho}{2}}}{4\sqrt[]{2\pi}}\cos(\theta)|^{2}.$$</p>
<p>I certainly know ab... | 6,369 |
<p>I'm a mathematics student trying to grasp some basics about wave propagation. A sentence I find very often in introductive physics textbooks is the following: </p>
<blockquote>
<p>In a wave, energy is proportional to amplitude squared.</p>
</blockquote>
<p>This is something I would like to understand better in t... | 351 |
<p>Can cloud charge imbalance be used as an energy source?</p>
<p>First off quite some energy must be present in clouds: a lightning path is quite long, and electrical breakdown of air requires about 1MV/m. Most (many, smaller) electric discharges are not seen because they occur within clouds. The electric energy buil... | 6,370 |
<p>Are there any good video lectures for learning quantum mechanics at the level of Griffith?</p> | 6,371 |
<p>I'm not well-versed in physics, so I hope you'll forgive me if this question is significantly off the mark.</p>
<p>I'm interested in the predominant frequencies of light over the course of one day. My understanding is that as the sun rises and falls, the atmosphere absorbs differing amounts of light, and that is re... | 6,372 |
<p>I've come across this article: <a href="http://pubs.acs.org/doi/abs/10.1021/nn4037706" rel="nofollow">Fluorescent Imaging of Single Nanoparticles and Viruses on a Smart Phone</a>.</p>
<p>And what is the theoretical limit for such smartphone extension? And how that limit can be computed (same as for microscope $\sim... | 6,373 |
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