question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>I want to simulate and test set of <strong>2D designs</strong> that basically have <strong>pulley/gear/chain-linked</strong> systems under Gravity (For e.g. to check how a pulley would rotate given particular weights, of course I'm not talking about such small systems, but systems where different pulleys/gears/weigh... | 5,923 |
<p>I am having trouble understanding the origin of the bosonic stimulated emission. How can I qualitatively understand why bosons Boson's attract each other into similar quantum states.</p>
<p>The furtherst I was able to get was to simulate the feedback process, in my mind, but I don't have the foggiest of ideas why t... | 5,924 |
<p>Equation of continuity says us that if we insert some fluid in a tube, the same amount of fluid will come out from the other end. If we make a small hole in a hose pipe, water will come out with a great speed. The bigger the hole, the slower the speed. This is a direct consequence of the equation of continuity.</p>
... | 913 |
<p>Is there any fundamental physical reason (thermodynamics/entropy?) behind the fact that there doesn't exist home appliance for fast cool down of food/drinks?</p>
<p>I know that there are some methods (liquid nitrogen, etc.) used in the kitchen, but I mean something much more common, like microwave oven but with opp... | 5,925 |
<p>What exactly do people mean when they talk about the scale dependence of the effective potential ($V$)? I explain the motivation for my question (and hence my confusion) below. Please correct me as appropriate.</p>
<hr>
<p>If one defines the effective potential as the non-derivative part ($p^2 \rightarrow 0$) of t... | 5,926 |
<p>I am given an initial x and y position and initial velocity and I was asked to graph the trajectory in 1 second intervals.</p>
<p>This is what I have so far:</p>
<p>If $x_0 = 1, v_{0x} = 70, y_0 = 0, v_{0y} = 80, a_x = 0, a_y = -9.8$, and time will be 0,1,2,3... and so on.</p>
<p>Using these equations on every se... | 7 |
<p>Assume an ideal board, supported by two joists. Where should those two joists be optimally placed?</p>
<p>Instinctively, I'd say at somewhat less than 25% and somewhat more than 75% of the extend of the board.</p>
<p>Presumably this also depends on whether the board can move freely with respect to the joists, or w... | 5,927 |
<p>Can anyone suggest a video or book that will allow the layman to grasp physics concepts in a conceptual manner? </p> | 5,928 |
<p>How does physics scattering experiments relate to real life? And what does the scientist gain from such experiments? I am having a hard time figuring the answer out. Please help.</p> | 5,929 |
<p>I understand NASA is now experimenting with a tweaked Alcubierre drive.</p>
<p>Apperantly some physicists predict crazy heat (hotter than the sun) inside the warp bubble caused by Hawking radiation (recent paper by Carlos Barceló, Stefano Finazzi, and Stefano Liberati).</p>
<p>One of the biggest problems with nucl... | 5,930 |
<p>I have always heard that the Earth, due to its structure, cannot explode. Now, I'm quite fascinated by astronomy physics but I admit I only hold some more than basic knowledge. </p>
<p>In any case, even though I have interiorized this concept, I have no basis to prove it. If you search on the internet, you get both... | 5,931 |
<p>Witten's 1981 paper <a href="http://www.sciencedirect.com/science/article/pii/0550321381900213">"Search for a realistic Kaluza-Klein theory"</a> is frequently cited for its observation that, in a compactification of d=11 supergravity on a manifold with SU(3) x SU(2) x U(1) isometry, left-handed and right-handed ferm... | 5,932 |
<p>Do quantum states contain exponentially more information than classical states? It might seem so at first sight, but what about in light of <a href="http://www.scottaaronson.com/talks/advucsb.ppt">this talk</a>?</p> | 5,933 |
<p>The <a href="http://en.wikipedia.org/wiki/Anthropic_principle">anthropic principle</a> is based upon Bayesian reasoning applied to the ensemble of universes, or parts thereof, conditioned upon the existence of conscious observers. That still leaves us with the problem of determining the prior probabilities. This is ... | 5,934 |
<p>I read that the non-commutativity of the quantum operators leads to the <a href="http://en.wikipedia.org/wiki/Uncertainty_principle#Mathematical_derivations">uncertainty principle</a>.</p>
<p>What I don't understand is how both things hang together. Is it that when you measure one thing first and than the other you... | 923 |
<p>I was reading Wikipedia which stated </p>
<blockquote>
<p>....Voyager 1's current relative velocity is 17.062 km/s, or 61,452 kilometres per hour (38,185 mph).....</p>
</blockquote>
<p>It travels away from sun. So sun's gravity must slow it down. What propels Voyager to that speed?</p> | 5,935 |
<p>Schwarzschild singularities are described by the Kantowski-Sachs metric with a contracting S<sup>2</sup>. Of course, T-duality doesn't apply to S<sup>2</sup>. But what about a Kasner-type singularity with two contracting spatial dimensions compactified over a torus T<sup>2</sup>, and an expanding spatial dimension? ... | 5,936 |
<p>It is known that pure heavy water will quickly get contaminated by light hydrogen atoms if exposed to air due to isotope exchange.</p>
<p>Does the same thing happens when heavy water is stored in plastic container, which also contains light hydrogen atoms?</p> | 5,937 |
<p>Two towns are at the same elevation and are connected by two roads of the same length. One road is flat, the other road goes up and down some hills. Will an automobile always get the best mileage driving between the two towns on the flat road versus the hilly one, if operated by a perfect driver with knowledge of ... | 5,938 |
<p>It might seem obvious but i can't imagine how is gravitational pull is different from acceleration due to gravity?</p> | 5,939 |
<p>How do the wheels of a train have sufficient grip on a metal track? I mean both of the surfaces are smooth (and not flexible) and it is okay if there is no inclination, but how about on an inclined track?</p> | 5,940 |
<p>We all learn in grade school that electrons are negatively-charged particles that inhabit the space around the nucleus of an atom, that protons are positively-charged and are embedded within the nucleus along with neutrons, which have no charge. I have read a little about electron orbitals and some of the quantum me... | 132 |
<p>This probably is dumb question, but it has been giving me issues for days.
I was thinking about a point of mass m in a circular orbit around a planet. The question is: giving a radial impulse, what is the change in the shape of the orbit? Will it change in another circular orbit? Or maybe will undergo a spiral moti... | 5,941 |
<p>I am a layman. I am aware that the <a href="http://en.wikipedia.org/wiki/Alcubierre_drive" rel="nofollow">Alcubierre Drive</a> has not yet been proven to be possible, but there is something about the concept itself that I am confused about. If there is no movement within the bubble, how is time measured inside the b... | 5,942 |
<p>What are the advantages/disadvantages of a transmission vs a reflection grating? It seems like a transmission grating would be easiest to use. I'm trying to get a spectrum from Thomson scattered light in a plasma. The broader the spectrum of the scattered light, the hotter the plasma. It's a weak effect, so it's im... | 5,943 |
<p>I am calculating for many hours and I am really confused with this exercise.</p>
<p>Consider a comoving observer sitting at constant spatial coordinates$(r∗,θ∗,φ*)$, around a Schwarzschild black hole of mass $M$. The observer drops a beacon into the black hole (straight down, along a radial trajectory). The beacon ... | 5,944 |
<p>How does a magnifying glass work? I know it creates a virtual image of the observed object but how is it possible that humans can see the virtual image?</p> | 209 |
<p>Reason behind <a href="http://en.wikipedia.org/wiki/Canonical_quantization" rel="nofollow">canonical quantization</a> in QFT?</p>
<p>In the scalar field theory we simply promote the scalar field, $\phi(x)$ to a set of operators: $\hat{\phi}(x)$. What is the reason behind this?</p> | 5,945 |
<p>I would like to have an image (in any kind of space), where I see the path of a "light" source. In my understanding the most common, directed source would be a laser pointer. </p>
<p>a) Is this correct? If not, what would be an other option?</p>
<p>As far as I know, to be able to "see" the path of the light, the m... | 5,946 |
<p>Trick dice have been used in gambling and magic shows. These are dice that, when rolled, will land with a preferred number facing upwards. This makes the result of rolling the dice non-random.</p>
<p>I was able to find a few ways to make trick dice, and I'm sure there are many more methods.</p>
<ol>
<li><a href="h... | 5,947 |
<p>So far 20 <a href="http://en.wikipedia.org/wiki/Synthetic_element">synthetic elements</a> have been synthesized. <strong>All are unstable</strong>, decaying with half-lives between years and milliseconds.</p>
<p>Why is that?</p> | 5,948 |
<p><a href="http://en.wikipedia.org/wiki/Kramers_theorem" rel="nofollow">Kramers theorem</a> rely on odd total number of electrons. In reality, total number of electrons is about 10^23. Can those electrons be so smart to count the total number precisely and decide to form Kramers doublets or not? </p> | 5,949 |
<p>Consider an explosion which is taking place in a vacuum, The exploding object is very small with a huge amount of energy and high density (like a big bang explosion) and the object explodes from the energy internally. I wanted to know how the mass is going to distribute after huge explosion in every direction. Does ... | 5,950 |
<p>What causes <a href="http://youtu.be/EM69cCGZF8o" rel="nofollow">those radiation readings</a> in my radiation meter (See the linked video)? Metal pieces were magnetized.</p>
<p>Used radiation detector is <a href="http://rads.stackoverflow.com/amzn/click/B00051E906" rel="nofollow">RADEX RD1503</a>. "Radiation" is no... | 5,951 |
<p>I am not a technical guy and I have no scientific knowloedge in <code>physics</code> but I have been reading books, watching videos in order to understand our cosmology and existance. Forgive me if I ask nonsense questions, if I do I'd do it because of my lack of knowledge.</p>
<p>As we all know <code>gravitational... | 5,952 |
<p>If non-zero cosmological constant interpreted as a repulsive field, what would be the properties of the excitation of such field, i.e. the particle which serves as the field's quantum?</p>
<p>What would be its spin, mass, possible interactions and other properties?</p> | 5,953 |
<p>In many textbooks it is said that mass renormalization of the electron mass is only logarithmic $\delta m \sim m\, log(\Lambda/m)$ because it is protected by the chiral symmetry.
I understand that in case of massless fermions to keep them massless in the renormalization procedure it must be like this. Or differently... | 5,954 |
<p><img src="http://i.stack.imgur.com/fuDZG.png" alt="enter image description here"></p>
<p>In the solution, it says we have $dr/dt= -V$ (polar coordinates)
How? I can't see how this can be possible, we know that $r(t)=V/\omega(t)$, and that's it.</p> | 5,955 |
<p>The unit for angular acceleration $\alpha$ is:</p>
<p>$$\mathrm{rad/s^2}$$</p>
<p>The unit for torque is $\mathrm{Nm}$:</p>
<p>$$\mathrm{kg\ m^2/s^2}$$</p>
<p>And their relationship with Inertia is:</p>
<p>$$I = \tau/\alpha$$</p>
<p>So shouldn't the unit for for Inertia be:</p>
<p>$$\mathrm{kg\ m^2/rad}$$</p>... | 210 |
<p>If we touch the live wire and ground at the same time, we will get a shock. But the current goes from live to ground and not to neutral i.e, circuit is open. Then how can we get a shock?</p>
<p><img src="http://i.stack.imgur.com/fLKbj.png" alt="Image"></p>
<p>This is the same circuit: will the current flow?<br>
<i... | 5,956 |
<p><--burst of thrust------|ME in a ship>----->>--<<--laser radar--<<---->>---||destination</p>
<p>In the above, I imagine myself in a ship, marking my speed to a far off destination with laser radar. In addition, someone at the destination is clocking me as well with a separate laser.</p>
<p>So, movi... | 5,957 |
<p>Suppose that $U(3)$ was the gauge group. We can decompose this as
$U(3)=U(1)\times SU(3)$,
which implies that in addition to the $SU(3)$ that has eight generators corresponding to eight gluons, there would be an additional generator for $U(1)$.</p>
<p>Would that generator behave like a photon? (no self interaction ... | 5,958 |
<p>This is really a question more about mining ventilation than true "physics." </p>
<p>I occasionally explore a southwest desert mine, but am aware of the hazards - typically passing over half a dozen vintage mines as unsafe (including anything vertical) before finding one stable enough and acceptable for exploration... | 5,959 |
<p>According to a website, $T_3 = T_2 + T_1$. Also, the rope and pulley device are mass less. But I don't really understand this. Let me try and explain how I see the problem.</p>
<p>$M_2$ receives tension in the up direction. This tension is the result of the resultant force of $M_1$ on the rope.</p>
<p>$M_1$ rec... | 5,960 |
<p>I'm working on a problem in 3d field theory and I'm confused about how to write the superfields. Specifically, I'm not sure if the signs and coefficients of terms are purely a matter of convention or if they need to be chosen more carefully. </p>
<p>For example in <a href="http://arxiv.org/abs/0806.1519" rel="nofol... | 5,961 |
<p>Everyone knows that the mass of a system is less than the mass of its components, with the equation:</p>
<p>$M = \sum_i m_i - BE(M) $</p>
<p>Now, if we consider a general decay, lets say</p>
<p>$A \rightarrow \sum_i B_i$</p>
<p>then, for the conservation of the first component of the four-vector momentum we obta... | 5,962 |
<p>What is the term used to describe the behaviour of (for example) a water droplet in free fall when it has reached a certain speed and then the force on the droplet causes the larger droplet to disperse into many smaller sized droplets. This also occurs in a Taylor Cone when using electrostatic spray. The charge buil... | 5,963 |
<p>Maybe mine is a silly question, but are there <strong>mathematical similarities</strong> or <strong>common roots</strong> between the <a href="http://en.wikipedia.org/wiki/Christoffel_symbols" rel="nofollow">Christoffel symbols</a>:</p>
<p>$ \nabla - \partial = \Gamma $</p>
<p>and the <a href="http://en.wikipedia.... | 5,964 |
<p>I'm looking at a way to prove that one recovers, under ad hoc assumptions, classical mechanics from quantum theory. Usually, we can find in textbooks that the propagator </p>
<p>$K(x,x_0;t)=\langle x|e^{-i \hat H t/\hbar}|x_0\rangle$ </p>
<p>is given in the classical limit by using the path integral formulation </... | 5,965 |
<p>What is the difference between Quantum Physics, <a href="http://en.wikipedia.org/wiki/Quantum_theory" rel="nofollow">Quantum Theory</a>, <a href="http://en.wikipedia.org/wiki/Quantum_mechanics" rel="nofollow">Quantum Mechanics</a>, and <a href="http://en.wikipedia.org/wiki/Quantum_field_theory" rel="nofollow">Quantu... | 5,966 |
<p>This is the last part of a derivation of the equation for an ideal gas undergoing reversible adiabatic expansion. I'm trying to prove that $T V^{\gamma-1}$ is constant, but my result is that $T V^{1-\gamma}$ is constant. Where am I going wrong?</p>
<p>I don't know what notation is standard, so please tell me if I s... | 5,967 |
<p>I used to have a vague feeling that the residue theorem is a close analogy to 2D electrostatics in which the residues themselves play a role of point charges. However, the equations don't seem to add up. If we start from 2D electrostatics given by $$\frac{\partial E_x}{\partial x} + \frac{\partial E_y}{\partial y} =... | 5,968 |
<p>If temperature makes particles vibrate faster, and movement is limited by the speed of light, then temperature must be limited as well I would assume. Why there is no limits?</p> | 237 |
<p>As I remembered, at the 2 poles of a battery, positive or negative electric charges are gathered. So there'll be electric field existing within the battery. This filed is neutralized by the chemical power of the battery so the electric charges will stay at the poles.</p>
<p>Since there are electric charges at both ... | 78 |
<p>This question arises in a somewhat naive form because I am largely unfamiliar with String Theory. I do know that it incorporates higher space dimensions where I shall take the overall dimensionality to be 10 in this question, for concreteness. Now the traditional <a href="http://en.wikipedia.org/wiki/Penrose%E2%80%9... | 5,969 |
<p>It seems like everything in the universe is in motion, at least relative to some other object. That leads me to believe that all objects are in motion. But how do we measure motion when we are talking about galaxies, is there any reference point that's not moving?</p> | 5,970 |
<p>I am a graduate student in experimental physics, currently writing up my dissertation and beginning to apply to post-doc positions. While it is very easy to find out about open positions in my particular sub-field (via various mailing lists), it is more difficult to find out about potentially interesting positions... | 5,971 |
<p>I'm working with an electronic temperature logger that is being affected by heat generated internally.</p>
<p>How does one come up with a calibration equation to calculate a more accurate reading of ambient temperature based on what the temperature sensor reads, taking into account its own power consumption?</p>
<... | 5,972 |
<p>Suppose an infinitely long cylindrical shell of radius $a$ carries a surface charge density $\sigma_0$ and is surrounded by a coaxial cable of inner radius $b$ and outer radius $c$ with uniform charge density $\rho_0$ such that the combined system is neutral.</p>
<p>I am asked to calculate the electrostatic energy ... | 5,973 |
<p>When you are sitting in a room where there is a source of bad smell, such as somebody smoking or some other source of bad smell, it is often a solution to simply move to another spot where bad smell is not present. Assuming you are not actually the source of the smell, this will work for a while until you notice the... | 5,974 |
<p>In the book "Reflections on Relativity" by Kevin Brown, there is a chapter called "Relatively Straight", in which he derives the geodesic equations using the Euler equation. <a href="http://mathpages.com/rr/s5-04/5-04.htm" rel="nofollow">Online version</a></p>
<p>Just after the second mention of the Euler equation... | 5,975 |
<p>Plasma consists of positive(ions) and negative(electrons) charges. Ions repel each other, so do the electrons, in the mean time ions attract electrons and vice versa, what will be the net result? Does the plasma tend to collapse or expand or stay in constant density? Why is it stable? </p> | 5,976 |
<p>When someone comes in from the cold to a heated room, it sometimes feels like there is coldness radiating away from that person. Is there a sense in which we can say that coldness radiates similarly to heat radiation? Does it make sense to have a theory of thermodynamics of coldness in which heat is replaced with co... | 5,977 |
<p>In classical mechanics, there are three types of invariance: invariance, form invariance and gauge invariance.
I am looking for a precise definition of these terms, but all I can find are sentences like "a physical law is form invariant if the form of the law does not change under coordinate transformations" or "a q... | 5,978 |
<p>Can we scatter the lightning before it hits the ground?Can we scatter the lightning by connecting many wires to a lightning rod?</p> | 5,979 |
<p>I am currently working on a (functional) analysis problem refining Pekar's Ansatz (or adiabatic approximation, as it is called in his beautiful 1961 manuscript "Research in Electron Theory of Crystals"). </p>
<p>Anyways, I have two related questions, which the members of this community may find simple. </p>
<p>The... | 5,980 |
<p>I'm trying to figure out how much distance does a ball of balsa wood covers until reaching terminal velocity, being released from a bottom of a pool.</p>
<p>To my understanding, I need to first figure out the terminal velocity. For that, I take:</p>
<p>$$F_\text{drag} + mg = F_\text{buoyancy}$$</p>
<p>$$F_\text{d... | 5,981 |
<p>Somehow when I google about the nuclear bombs I find a lot of books and resources that seem to explain everything about how those bombs are made. But sometimes I often hear that countries that want to make them usually don't have the technology to do them. But I always questioned myself, as why?! I mean it looks to ... | 5,982 |
<p>Newton's second law says $F=ma$.
Now if we put $F=0$ we get $a=0$ which is Newton's first law.
So why do we need Newton's first law ? </p>
<p>Before asking I did some searching and I got this: Newtons first law is necessary to define inertial reference frame on which the second law can be applied.</p>
<p>But why c... | 5,983 |
<p>This is really a one-and-a-half part question.</p>
<p>I know that when paint is mixed with a solvent or used with a primer, it sometimes wrinkles. As I understand, a key physical phenomena here is a non-uniform evaporation of the primer or solvent that gives rise to different evaporation rates at the paint surface.... | 5,984 |
<p>A large electroscope is made with "leaves" that are $78$-cm-long wires with tiny $24$-g spheres at the ends. When charged, nearly all the charge resides on the spheres.</p>
<p>If the wires each make a $26^{\circ}$ angle with the vertical, what total charge Q must have been applied to the electroscope? Ignore the ma... | 5,985 |
<p>what is the key difference between the windings of the electric motor and electric generator?</p> | 5,986 |
<p>I've read that maximally entangled qubit states are a good "unit" of bipartite entanglement since it is possible to create any other entangled state from them using local operations and classical communication (LOCC) provided sufficiently many copies are available. What would the protocol be to construct a maximally... | 5,987 |
<p>I am working on an algorithm for a real-time simulation. </p>
<p>I would like to calculate to extremely permissive tolerances approximate values for the stress within a 2D geometry. It will not be difficult to triangulate so we can assume a mesh or grid is available. </p>
<p>From what I have read, it seems that in... | 5,988 |
<p>In a Physics lesson today our teacher performed a demonstration to show how quinine in tonic water glows blue when under UV light. He showed us the same demonstration using water in a Pyrex beaker, and with just the Pyrex beaker itself in order to compare the effects.</p>
<p>Under UV light the Pyrex beaker glowed o... | 5,989 |
<p>There are proofs in the literature that QFT including microcausality is <em>sufficient</em> for it not to be possible to send signals by making quantum mechanical measurements associated with regions of space-time that are space-like separated, but is there a proof that microcausality is <em>necessary</em> for no-si... | 717 |
<p>How can I diagonalize the following operator?</p>
<p>$$\lambda \hat{\vec{\sigma}}\cdot\vec{r}$$</p>
<p>where $\lambda$ is a real constant, $\hat{\vec{\sigma}}=(\hat{\sigma_{x}},\hat{\sigma_{y}},\hat{\sigma_{z}}) $ is the Pauli operator and $\vec{r}=(x,y,z)$ is the position operator.</p> | 5,990 |
<p>If you go to the Atlas experiment <a href="http://atlas.ch/" rel="nofollow">http://atlas.ch/</a> and click the status button, there's an AFS reading at the bottom with a current value</p>
<p>50ns_228b+1small_214_12_180_36bpi_8inj</p>
<p>The 50ns seems to refer to the bunch spacing, the 228b the number of bunches, ... | 5,991 |
<p>Physically, quantum entanglement is ranged from full long-range entanglement (Bose-Einstein condensate), described by a basis of states that look like this:</p>
<p>$$ |\Psi\rangle = |\phi_{i_{0} i_{1} ... i_{N}}\rangle $$</p>
<p>to full-decoherence (a Maxwell-Boltzmann ideal gas) which a basis of states that look ... | 5,992 |
<p>How much body temperature can a motor withstand along with the ambient temperature to work without failing?</p> | 5,993 |
<p>Can the value of Newton's <a href="http://en.wikipedia.org/wiki/Gravitational_constant" rel="nofollow">Gravitational Constant</a> $G$ be measured within a stably bound atom?</p>
<p>PLEASE NOTE: Since scattering experiments do not involve stably bound systems, their results are not germane to the specific question a... | 5,994 |
<p>Does the mass of both the parent object, and the child object affect the speed at which the child object orbits the parent object?</p>
<p>I thought it didn't (something like $T^2 \approx R^3$) until I saw an planet on the iphone exoplanet app, that is closer to it's star than a planet in another system, yet takes l... | 375 |
<p>There are two experiments that are often used to explain Quantum Mechanics: the two-slit experiment and the EPR paradox. I am curious what would happen if you combined them.</p>
<p>Imagine an experiment where you fire pairs of entangled particles at two simultaneous two-slit setups. If you used detectors, you cou... | 5,995 |
<p>I have a hard time understanding why light waves of different wavelengths diffract in a different manner. According to Huygens' principle, every point on the wavefront is a source of a secondary wave. So if we have a white light going through, say, a single slit (light rays parallel to each other and perpendicular t... | 5,996 |
<p>Please refer to the question "Resolution of the EPR paradox using relativity of simultaneity" I hope that this question will be clearer.</p>
<p><strong>EPR photon experiments are a paradox for scientists. Can someone tell me why?</strong></p>
<p>Distances and traveling time of photons are always measured on the ba... | 5,997 |
<p>I know there are two ways of measuring the angle of a prism with a goniometer:</p>
<blockquote>
<p>let the collimator shine (monochromatic) light on 2 sides of the prism and measure the angle between the 2 reflected lightbeams. </p>
</blockquote>
<p>or </p>
<blockquote>
<p>Let the lightbeam hit one side of ... | 5,998 |
<p>I'm studying a problem and I encountered a strange problem:</p>
<blockquote>
<p><em>When a ball bounces how much time does the ball spend while touching the floor?</em></p>
</blockquote>
<p>To be more clear I suppose that when a ball bounces the actual bounce can't start EXACTLY when the ball touches the floor b... | 5,999 |
<p>In page 488 of Peskin and Schroeder, it is stated (emphasis mine):</p>
<blockquote>
<p>It is not difficult to check using (15.27) and (15.21) that, even for <em>finite</em> transformations, the covariant derivative has the same transformation law as the field on which it acts.</p>
</blockquote>
<p>I was trying t... | 6,000 |
<p>In a badly-adjusted (too cold) fridge, I notice that things like celery & lettuce are more likely to be spoiled by becoming frozen if they're put on a <em>middle</em> shelf, rather than the salad drawer at the <em>bottom</em>.</p>
<p>I realise the salad drawer is "enclosed". But it's far from air-tight, so over... | 6,001 |
<p>I tried to solve a problem using two different ways and I had some trouble, the problem is:</p>
<p>We define a symmetry transform of the expected value of $\vec{P}$ like this:
$$\langle \psi|\vec{P}|\psi \rangle \rightarrow \langle \psi|\vec{P}+m\vec{V_0}|\psi \rangle$$</p>
<p>being $\vec{V_0}$ a constant vector.<... | 6,002 |
<p>I was reading Planetary Motion (page 117) in Barry Spain's <em>Tensor calculus</em>, and stupidly enough, I didn't understand this. The equations are :</p>
<p>$$\frac{d^2\psi}{d\sigma^2} + \frac{2}{r}\frac{dr}{d\sigma}\frac{d\psi}{d\sigma} = 0,$$</p>
<p>$$\frac{d^2t}{d\sigma^2} + \frac{2m}{c^2r}\left(1-\frac{2m}{c... | 6,003 |
<p>I am making a speech about <a href="http://www.google.com/search?q=miku+hatsune+3d+hologram" rel="nofollow">Miku Hatsune 3D hologram</a>, and I would like to know how they are made! I love Miku and Len...(drools) please help by explaining!</p> | 6,004 |
<p>When applying a force outside of the center of mass of the body, the body will get both linear and angular momentum. Right?</p>
<p>Does the linear velocity from this force equal to the linear velocity from the same force, which is applied on the center of mass?</p>
<p>$$v_{\text{center}} = v_{\text{non-center}}\qu... | 6,005 |
<p>I've got a question about derivation of RG equations made in "Gauge theory of elementary particles" by <a href="http://rads.stackoverflow.com/amzn/click/0198519613" rel="nofollow">Cheng & Li</a>. At page 79 (page 97 in Russian edition) they represent bare parameters ($\mu_0, \, \lambda_0, \, \phi_0$) as Laurent ... | 6,006 |
<p>A theory among scientists says that quantum fluctuations caused the big bang and created the universe. This seems plausible to me. </p>
<p>What I can't grasp yet is how a quantum fluctuation can even start without an existing universe. Aren't all physical laws created with the universe? I understand that there is n... | 6,007 |
<p>For a spinor on curved spacetime, $D_\mu$ is the covariant derivative for fermionic fields is
$$D_\mu = \partial_\mu - \frac{i}{4} \omega_{\mu}^{ab} \sigma_{ab}$$
where $\omega_\mu^{ab}$ are the spin connection.
And the transformation of spin connection is very similar to gauge field.
So is there any relationship be... | 865 |
<p>When you energise a taut string, the following resonant modes of vibration occur:</p>
<p><img src="http://i.stack.imgur.com/pA0iS.jpg" alt="enter image description here"></p>
<p>Plotting on the frequency domain, you can see their corresponding frequencies:</p>
<p><img src="http://i.stack.imgur.com/tPSI5.jpg" alt=... | 6,008 |
<p>Sorry for my ignorance, but does the result of <a href="http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment" rel="nofollow">Michelson-Morley experiment</a> have some explanation? Is there some reason why light speed in vacuum is maximum or we just find it by experiments?</p> | 6,009 |
<p>The integral,</p>
<p>$$ \iint_{\mathbb{R}^{2+}}\frac{xy}{1+x+y} \mathrm{d}y \, \mathrm{d}x$$</p>
<p>possesses an overlapping divergence when $ x \to \infty $ and $ y \to \infty $. However, under a change of variables to polar coordinates,</p>
<p>$$ \int_{0}^{\infty}dr\int_{0}^{2\pi}du \frac{r^{3}\sin(u)\cos(u)}{1... | 6,010 |
<p>Here is the question as given in my textbook:</p>
<blockquote>
<p>Find the distance of the object from a concave mirror of focal length 10 cm so that the image size is 4 times the size of the object.</p>
</blockquote>
<p>The solution in my textbook has the following data stated:</p>
<p>$u=-x$ as it is assumed t... | 6,011 |
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