dialog listlengths 4 30 | title stringlengths 15 150 | category stringclasses 14 values | dialog_time stringdate 2016-01-21 01:59:30 2018-07-01 01:34:46 |
|---|---|---|---|
[
{
"message": "<blockquote> A cube of mass M rests tilted against the wall as shown (see below). There is no friction between the wall and the cube, but the friction between the cube and the floor is just sufficient to keep the cube from slipping. When $0\\lt\\theta\\lt 45^\\circ$ find the minimum coefficient o... | Torque with 2D center of mass | physics | 2017-05-02T22:39:04.717 |
[
{
"message": "In general relativity, is it proper to say that mass curves the three spatial dimensions (x1, x2, x3) and also that mass curves the fourth dimension x4?",
"role": "user"
},
{
"message": "As @Jaywalker said you are essentially right. But careful that space and time are mixed in in Gener... | In general relativity, is it proper to say that mass curves the three spatial dimensions and also that mass curves the fourth dimension? | physics | 2017-05-02T23:39:59.287 |
[
{
"message": "Having defined the phase space distribution function $f(\\textbf{r},\\textbf{p},t)$ in $\\mu-$space, one can express the information that there are $N$ particles in the volume $V$ through the condition \\begin{equation}\\int f(\\textbf{r},\\textbf{p},t) d^3\\textbf{r}d^3\\textbf{p}=N\\end{equation... | Kolb and Turner's expresion for number density Eqn. (3.46) and pressure in Eqn. (3.48) | physics | 2017-05-03T15:00:16.963 |
[
{
"message": "I am working on a car simulation game and I need to know how to calculate a vehicle's velocity if the gas pedal was floored and the car started accelerating from rest with some slippage in the wheels. So, is the traction force completely gone, or it decreases? And how long will the wheels keep sli... | How to calculate a wheel's linear velocity if there is slipping | physics | 2017-05-03T23:56:52.693 |
[
{
"message": "<a href=\"https://i.stack.imgur.com/PqNC5.jpg\" rel=\"nofollow noreferrer\">I have been given the above question, with the solution, <a href=\"https://i.stack.imgur.com/q9BUV.jpg\" rel=\"nofollow noreferrer\">One correction I observed from the answer was, in question c part would be acceleration ... | Pulley System - How the blocks will move? | physics | 2017-05-04T03:32:39.947 |
[
{
"message": "In a \"slowly\" expanding Universe, suppose the number density of a particle species $A$ undergoing a equilibrium decay $A\\to B+C$. The equilibrium number density depletes with the expansion and the consequent fall of temperature but in equilibrium. For example, the number density of the relativi... | How does in an expanding universe the equilibrium number density change with temperature? | physics | 2017-05-04T07:44:19.373 |
[
{
"message": "How do we deduce Snell's law using Fermat's principal in case of metamaterials? <br> <br> Metamaterials have negative refractive index. This makes the refracted ray of light bend on same side of normal as incident ray. <br> <br>But according to Fermat principle, the light could have taken a shorte... | Metamaterial : Snell's law and Fermat principle | physics | 2017-05-04T15:30:40.910 |
[
{
"message": "I am a biologist . I \"modelled\" the behavior of a fully streched dipeptide using MD. In another exploration, I minimized the energy of the streched dipeptide. I used the same forcefield and implicit water for both models.The 2 final dipeptides have different configurations, and their energy (whi... | Molecular Dynamics vs energy minimization in protein folding | physics | 2017-05-04T20:45:01.630 |
[
{
"message": "How does the Lippmann-Schwinger equation and the scattering amplitude generalize when we include spin? Also, how does the scattering amplitude up to the first Born approximation change if we include spin? EDIT: If somebody could include the scattering amplitude with spin, it would be ideal. Also,... | Lippmann-Schwinger equation and Scattering amplitude with spin | physics | 2017-05-04T23:22:52.540 |
[
{
"message": "How does the Lippmann-Schwinger equation and the scattering amplitude generalize when we include spin? Also, how does the scattering amplitude up to the first Born approximation change if we include spin? EDIT: If somebody could include the scattering amplitude with spin, it would be ideal. Also,... | Lippmann-Schwinger equation and Scattering amplitude with spin | physics | 2017-05-04T23:22:52.540 |
[
{
"message": "A light string with a particle of mass $m$ at one end, wraps itself around a fixed vertical cylinder of radius $a$. The entire motion is in the horizontal plane(neglect gravity). The angular speed of the string (and the particle) is $\\omega_0$ when the distance of particle from point of contact b... | How to find the angular velocity and tension in the string? | physics | 2017-05-06T00:20:28.530 |
[
{
"message": "According to standard quantum mechanics, after a measurement, the original state will \"collapse\" to one of the eigenstate of the observable, and if one measures it immediately after , the result will be the same.Does the second measurement give the same result in experiment? Is there any real ex... | Quantum measurement in experiment | physics | 2017-05-06T12:18:55.503 |
[
{
"message": "Pardon the confusing title, but I'll try and rephrase what I'm asking. Longitudinal modes in a wavelength of light require the optical length of the cavity to be such that the wavelengths need to form two nodes at either end of the cavity - essentially starting and ending at the same effective 0 p... | What if the optical length of a cavity is not a half integer scalar of the standing wave wavelength? | physics | 2017-05-06T13:59:26.733 |
[
{
"message": "I often wonder about kinetic energy and potential energy. In physics, if a rock is on top of a hill, it has potential energy or kinetic energy that doesn't exist yet. Instead, is it safe to think of potential energy as instantaneous kinetic energy? If we were to graph it as kinetic energy over ti... | Can Potential energy be the same as instantaneous kinetic energy? | physics | 2017-05-06T18:13:05.693 |
[
{
"message": "The fusion triple product is a commonly used figure of merit to quantify the progress in fusion research, it is the product of plasma density $n$, temperature $T$ and energy confinement time $\\tau_E$. It can be used in combination with a power balance to formulate a criterion for ignition, which... | How to calculate the bremsstrahlung limit in the fusion triple product diagram? | physics | 2017-05-06T19:38:22.353 |
[
{
"message": "This question is inspired by Arnold's book (<a href=\"http://rads.stackoverflow.com/amzn/click/0387968903\" rel=\"nofollow noreferrer\">Mathematical Methods of Classical Mechanics). In chapter 2 he defines the diffeomorphism $g^t$ as the mapping $g^t: \\Bbb{R}^2 \\to \\Bbb{R}^2$ that propagates a ... | Undefined Phase Flow | physics | 2017-05-08T02:05:18.827 |
[
{
"message": "We can simulate the motion of atoms using a classical computer.Therefore, it seems we should be able to simulate quantum mechanical systems on classical computers.However, there still seems to be some mystery surrounding the collapse of the wave function upon measurement.Suppose we wanted to simul... | Thought experiment: Modeling/Simulating measurement of a qubit using a classical computer | physics | 2017-05-08T11:16:19.207 |
[
{
"message": "If you have a television that displays the image of a clockwise spiral on a white background, and you apply one side (pole) of a strong magnet such as a good size neodymium iron boron magnet - the image will shift in a rotational fashion to either the left, or the right. If you switch the pole, th... | Why does a television image rotate to the right when one side of the magnet is applied, and to the left when the other is applied? | physics | 2017-05-08T12:35:18.317 |
[
{
"message": "Accroding to this <a href=\"http://www.iflscience.com/technology/how-drop-seawater-graphene-generates-electricity/\" rel=\"nofollow noreferrer\">http://www.iflscience.com/technology/how-drop-seawater-graphene-generates-electricity/ webpage, voltage would be generated if droplets of seawater (whic... | Would seawater lose their ions after sliding across graphene | physics | 2017-05-08T20:04:46.167 |
[
{
"message": "I am studying quantum optics from Gerry and Knight's book. This question has to do with section 2.1 of the book, where a single mode light field in a cavity is quantized. The formal equivalence of a single-mode field and a harmonic oscillator of unit mass is established just by showing that the fo... | Quantization of single mode field in a cavity | physics | 2017-05-09T11:36:21.743 |
[
{
"message": "How do we find the energy momentum tensor as Noether charge for translations in curved spaces. This should still exist since the action is still an integral over space such that it it invariant under translations right?Attempt at a solutionOur Lagrangian will be of the form: $\\mathcal{L} = \\math... | Scalar field in curved spaces | physics | 2017-05-09T12:32:24.730 |
[
{
"message": "Some of the spotting scopes which are e.g. 70mm claim to magnify terrestrial objects at 75x. But yet they cannot produce sharp and clear images at even 30x-35x.While 90mm scopes can do a better job than them but still they stop producing clear view at higher magnification.So, I want to know is the... | What's the useful magnification for a scope with 70mm objective lens? | physics | 2017-05-09T14:37:27.753 |
[
{
"message": "If I am not mistaken, the Ives-Stilwell experiment measures the frequency of emitted light to test the relativistic doppler formula. Is there anything like this for light intensity? Have we measured the headlight effect? Anything like precision tests that are related to this would be interesting."... | Are there experiments that deal with the headlight effect? | physics | 2017-05-09T15:47:59.017 |
[
{
"message": "<a href=\"https://i.stack.imgur.com/T4AH0.png\" rel=\"nofollow noreferrer\">By Faraday's law, the flux is constant, so there will be no emf. But each electron in the metal sheet is moved at some speed, so it will experience a force, and as a result, electrons will accumulate at the edges of the me... | Why is there an emf induced across the width of a metal sheet when it is moved across a uniform magnetic field? | physics | 2017-05-09T23:18:45.180 |
[
{
"message": "In electrodynamics, the scar potential $\\phi$ and the vector potential $\\textbf{A}$ satisfy the equations $$\\frac{\\partial}{\\partial t}(\\boldsymbol{\\nabla}\\cdot\\textbf{A})+\\nabla^2\\phi=-\\frac{\\rho}{\\epsilon_0}$$ and $$\\boldsymbol{\\nabla}\\Big((\\boldsymbol{\\nabla}\\cdot\\textbf{A}... | Radiation gauge and choice of the gauge function | physics | 2017-05-10T07:10:48.537 |
[
{
"message": "How does one correctly calculate the second-order variation of an action? I have started an attempt at the calculation (restricting the scalar fields for simplicity), but I'm unsure how to proceed.Starting with the action for a free scalar field $$S[\\phi]=\\int\\;d^{4}x\\mathcal{L}=\\frac{1}{2}\\... | How to calculate second-order variations of an action? | physics | 2017-05-10T15:17:28.467 |
[
{
"message": "I took a stab at deriving the time dilation formula for velocity. This is entirely my own approach though I suspect it is nothing new/special in terms of how it is derived. Just wanted to have some fun and see if i could figure it out for myself. So I knew it was all based on the idea that the spe... | Derriving time-dilation formula for velocity | physics | 2017-05-10T23:26:53.543 |
[
{
"message": "We know that friction between two bodies helps charge them. How does, for example, a piece of scotch tape stuck on a wooden table (adhesive force), charge the scotch tape?",
"role": "user"
},
{
"message": "It is not the adhesive force that charges the tape. It gets the charge when the ... | How do adhesive forces provide charge to materials? | physics | 2017-05-11T12:36:28.697 |
[
{
"message": "In many texts, the non-relativistic (Newtonian) kinetic energy formula $$\\text{KE}_\\text{Newton} =\\frac{1}{2}mv^2$$ is referred to as a first order approximation of the relativistic kinetic energy $$\\text{KE}_\\text{relativistic} = \\gamma mc^2 - mc^2$$ The same is also said of the classical m... | Why is the Newtonian expression for kinetic energy called the "first order" approximation of the relativistic expression? | physics | 2017-05-11T14:52:18.837 |
[
{
"message": "Over the weekend I was (in over my head) discussing mass/energy and I proposed this thought experiment.Given two separate but equal quantities of matter - one being wood, the other being gasoline - do they both have the same total energy? I am being assured that the gasoline has more every than th... | Does this make sense from mass-energy equivalence standpoint? | physics | 2017-05-11T17:22:41.487 |
[
{
"message": "I see there have been a lot of questions about the big bang and did it start from a singular point etc. And i agree with the answers given, that the universe is infinite and is expanding about every point within it, like a grid where the space in between the points is expanding or stretching, that... | Universal Space Expansion | physics | 2017-05-11T22:25:45.677 |
[
{
"message": "<a href=\"https://i.stack.imgur.com/S3QY5.png\" rel=\"nofollow noreferrer\">When Bragg's law is explained, the word \"diffraction\" is used. But, as far as I see the picture above which is often added to the explanation, it seems what happens is not diffraction but just reflection.I believe diffra... | Why, in Bragg's law, is the word "diffraction" used? | physics | 2017-05-12T10:44:21.377 |
[
{
"message": "From what I understand I think if I construct the phase space by plotting $x$ component of momentum against $x$ for a quantum mechanical particle, I cannot specifically put a single point to mark the particle's state in that phase space. For that would mean I can state the position and momenta of ... | How can we represent uncertainty principle in phase space? | physics | 2017-05-12T16:00:21.513 |
[
{
"message": "In a Feynman diagram, the particles behave like free particles everywhere except at one of the vertex of the diagram. The vertex is the site for an interaction to occur.So, if we have an electron which emits and later absorbs the same photon, we already have 2 vertex in the diagram. But i think th... | Is a Feynman diagram for an electron emitting and later absorbing the same photon possible with just 2 vertex in the diagram? | physics | 2017-05-12T18:11:41.513 |
[
{
"message": "I have learned that the characteristic time for QCD process is about $10^{-24}s$, Then I wonder if there is a way to estimate the timescale for strong interactions?",
"role": "user"
},
{
"message": "The width of a <a href=\"https://en.wikipedia.org/wiki/Resonance_(particle_physics)\" r... | How to estimate the timescale for strong interactions? | physics | 2017-05-13T02:20:26.153 |
[
{
"message": "Note: this is NOT a question why current is the base unit as opposed to charge—that’s because measuring $1 \\ \\mathrm{ A }$ through a wire is easier to measure in a lab than is $1 \\ \\mathrm{ C }$ in free space; the question explores why electric units are chosen as base units in the SI in the f... | Why are electrical units (specifically, electrical current) considered a base unit? | physics | 2017-05-13T04:04:11.663 |
[
{
"message": "Note: this is NOT a question why current is the base unit as opposed to charge—that’s because measuring $1 \\ \\mathrm{ A }$ through a wire is easier to measure in a lab than is $1 \\ \\mathrm{ C }$ in free space; the question explores why electric units are chosen as base units in the SI in the f... | Why are electrical units (specifically, electrical current) considered a base unit? | physics | 2017-05-13T04:04:11.663 |
[
{
"message": "Is it possible for a person to physically jump a ladder off the ground while standing on the ladder? The ladder is leaning at 10 degrees and contacting a rough surface at 20 feet and the individual wanting to jump the ladder to move it to another location a foot away stands on the ladder at 18 ft ... | Jumping a ladder | physics | 2017-05-13T15:34:55.540 |
[
{
"message": "Thermodynamics neglects fluctuations and deals with average macroscopic quantities (which is also important for the extensity of extensive thermodynamics coordinates e.g., the internal energy ${\\rm U}$, entropy ${\\rm S}$ etc). On the other hand, the fluctuations cannot be neglected at the critic... | Can thermodynamics be relied at the critical point? | physics | 2017-05-13T17:55:38.680 |
[
{
"message": "My knowledge in aerodynamics is very limited as I am doing just an introduction to the subject, and so I may not understand very complex explanations. I know that at some point laminar flow becomes turbulent flow, but why is this, and why does this occur in less distance if the surface is rougher?... | Turbulent flow and Separated flow | physics | 2017-05-13T23:04:51.480 |
[
{
"message": "If relativity is symmetric, do the satellites in the GPS system see the earthbound clocks as running slow due to relativistic time dilation?How much slower does the satellite see the earthbound clock running as it passes overhead?",
"role": "user"
},
{
"message": "The <a href=\"http://... | If relativity is symmetric, do the satellites in the GPS system see the earthbound clocks as running slow due to relativistic time dilation? | physics | 2017-05-14T03:04:42.130 |
[
{
"message": "I was reading about different integrators that one might use to solve the system of differential equations which governs the $n$-body problem. I read that the Verlet integrator is time-reversible, and thus conserves energy. I don't understand why time-reversibility implies energy conservation.Supp... | Proof that Verlet integration conserves energy | physics | 2017-05-14T08:15:32.360 |
[
{
"message": "When we were in school, the teachers used to tell us that heat increases the kinetic energy of the particles (reflected in the temperature) until the boiling point is reached. Afterwards, all the heat goes into breaking the intermolecular bonds between the liquid particles until all of them change... | Why does temperature remain constant at the boiling point of the liquid? And what kind of an equilibrium is boiling? | physics | 2017-05-14T09:38:29.327 |
[
{
"message": "Calculating atomic spectra means to me that one takes a Hamiltonian neglecting some effects known to be present (any such Hamiltonian will always neglect something, be it relativistic effects or even quantum gravity) and tries to approximate its (math.) spectrum. I've only every seen this scheme a... | How well can we calculate atomic spectra from first principles? | physics | 2017-05-14T14:12:38.050 |
[
{
"message": "In cosmology, while deriving how the energy density dilutes with the scale factor one assumes $p=w\\rho$ with $w=0$ for the matter, $w=-1$ for vacuum energy and $w=1/3$ for the radiation. In know the energy density of radiation varies as $p=\\frac{1}{3}\\rho$. But I do not understand why is it tak... | Various values of $w$ in the equation $p=w\rho$ | physics | 2017-05-14T15:24:55.443 |
[
{
"message": "I'm new to the forum and I wish to say HELLO to all!I've studied physics long time ago and now I try to recall some notions. I've the following misunderstanding, can please somebody help me? Thanks!In Special Relativity I recall the following two definitions:proper length $L_0$: it is the length o... | Special relativity: A confusion between proper length and proper distance | physics | 2017-05-14T15:25:48.073 |
[
{
"message": "I was reading the following book/series of lectures located here <a href=\"http://isites.harvard.edu/fs/docs/icb.topic521209.files/QFT-Schwartz.pdf\" rel=\"nofollow noreferrer\">http://isites.harvard.edu/fs/docs/icb.topic521209.files/QFT-Schwartz.pdf; it's an introduction to quantum field theory. ... | Exact Photon Propagator in Quantum Electro-Dynamics | physics | 2017-05-15T02:55:48.250 |
[
{
"message": "According to <a href=\"https://en.wikipedia.org/wiki/Bernoulli%27s_principle#Misapplications_of_Bernoulli.27s_principle_in_common_classroom_demonstrations\" rel=\"nofollow noreferrer\">Wikipedia,<blockquote> A correct explanation of why the paper rises would observe that the plume follows the cu... | Why is a piece of paper lifted upward even when blown below? | physics | 2017-05-15T05:14:32.677 |
[
{
"message": "DM: dark matter; OM: ordinary matterI know that DM has a distribution which is mostly concentrated in the center of galaxies. This was mainly deduced by accounting for gravitational effects on the motion of galaxies which weren't due to any visible matter.1) a: What property of DM which isn't pres... | Why isn't Dark Matter distributed among ordinary matter? | physics | 2017-05-15T12:34:52.890 |
[
{
"message": "<blockquote> if two speakers are separete from each other by 5.25m and an observer is 50m away in the same line that on of the speakers. What type of interference exist? The speakers are in phase and have a frequency of 1.5khz.</blockquote>I have problems to resolve this exercise. The formul... | Problem in determining constructive or destructive interference of sound waves | physics | 2017-05-15T16:07:58.707 |
[
{
"message": "Calculate the magnetic field at the point $P$:<a href=\"https://i.stack.imgur.com/N33Pp.jpg\" rel=\"nofollow noreferrer\">For me, the contribution of the magnetic field due to the wire where it's inclined is going to be zero, because $\\vec{dl} \\times \\vec{r} = 0$ since the angle is going to be ... | Magnetic field - Application of Biot-Savart law | physics | 2017-05-15T23:11:44.040 |
[
{
"message": "I am having a bit of a conceptual issue with excitation and change of state. I understand that when a light hits a gas, some of the light may be absorbed by the gas to excite the atoms in the gas; the idea of absorption spectra. But where is this energy that excites the atom going? If we have wate... | Excitation of atoms (energy levels) and change of state | physics | 2017-05-16T00:56:33.427 |
[
{
"message": "I am programming a space game, and I put this on the physics stack exchange because I need some help in the physics behind it. Let's say there is a moving enemy ship - referred to as \"target\", and we want to lead our ship's torpedo to a point where the bullet will intercept the moving target. Be... | Bullet interception? | physics | 2017-05-16T04:24:57.413 |
[
{
"message": "Apparently one means of detecting WIMPs is to search for a photon ejected when one interacts with matter. If we don't know its mass or velocity and the weak interaction implies the absence of charge, why is a photon released?",
"role": "user"
},
{
"message": "You do not give a link for... | Search for WIMPs | physics | 2017-05-16T15:14:38.023 |
[
{
"message": "My problem is given by the following formulation:<blockquote> Determine the minimum velocity v of a particle at point P(0,-b), so that it can follow out a loop along a curve by the equation: $x^2/a^2+y^2/b^2=1$; The height of the loop is 2b above ground level; ground-level is by the coordin... | Minimum velocity to accomplish an elliptical loop; | physics | 2017-05-16T18:41:50.980 |
[
{
"message": "Does special relativity predict the possibility of particle creation? Is it due to the relativistic energy-momentum dispersion $$E^{2}=m^{2}c^{4}+p^{2}c^{2}$$ which shows that mass is simply a form of energy, and as such other forms of energy can be converted into mass energy, or equivalently, mas... | Special relativity and particle creation | physics | 2017-05-16T21:46:04.223 |
[
{
"message": "I am studying the multipole expansion of electromagnetic wave radiation pattern, and it is said that any fields can be decomposed into the spherical harmonics $Y_{lm}$.However, for $l=1$, which corresponds to a dipole, the spherical harmonics looks like a dumbbell, as shown in the attached picture... | The dipole radiation pattern and spherical harmonics $Y_{10}$ | physics | 2017-05-17T09:17:08.740 |
[
{
"message": "Can someone point me in the direction so that these questions can be solved? A hint would be enough.",
"role": "user"
},
{
"message": "The \"most general\" approach uses <a href=\"http://www.softschools.com/notes/ap_physics/kirchhoffs_rules_and_resistors_in_series_and_parallel/\" rel=\... | Equivalent resistance between A and B | physics | 2017-05-17T12:24:52.793 |
[
{
"message": "With a lab waveguide / horn antenna setup similar to image (without bends), we made the following measurements. Now we thought this could be used to demonstrate the observation of the inverse square law, but can't see how(?)SWR meter (dB setting), measured at various distances (d) : <pre><code> 0.... | Waveguide horn antenna & inverse square law | physics | 2017-05-17T13:50:09.560 |
[
{
"message": "I am aware that the everything with mass produces gravitational waves and the only reason why we don't detect them is because they are incredibly small. If gravitational waves act like every other wave then they should super impose. Since in the universe there are a large number of massive objects... | Gravitational waves detection | physics | 2017-05-17T17:19:36.603 |
[
{
"message": "Consider the Lagrangian for the type-I seesaw given by$$-\\mathcal{L}=\\bar{\\nu}_{L}m_DN_{R}+\\frac{1}{2}\\overline{(N_{R})^c}M_R N_{R}+\\text{h.c.}.$$ $\\bullet$ In this Lagrangian, what is the nature of $N_R$ field? I think it cannot be Majorana even though we write a Majorana mass for it becau... | Is $N_R$ a Majorana field in the Seesaw Lagrangian? | physics | 2017-05-17T17:49:04.950 |
[
{
"message": "at around 2.20 in <a href=\"https://www.youtube.com/watch?v=dm30ckh-pW8&ab_channel=CSIRO\" rel=\"nofollow noreferrer\">this video the woman says that if it doesn't work, you should try and turn the magnet around. I've tried it and the magnets do need to be facing each other with the same pole ... | Mini rail gun to build at home | physics | 2017-05-17T18:32:21.933 |
[
{
"message": "In spin orbit interaction, a magnetic field (internal ,I guess)comes into picture. So how this magnetic field is produced and by who - electron or nucleus?In my book, it says electric field is produced by nucleus . Due to this electric field, moving electron experiences magnetic field. I am not ab... | Which magnetic field is involved in spin-orbit interaction? | physics | 2017-05-17T19:43:04.723 |
[
{
"message": "Does interaction with physical slits in a double slit experiment indicate that the wavefunction is a real physical wave, as opposed to a mathematical abstraction? This question pertains to the psi ontology debate as described here <a href=\"https://arxiv.org/pdf/1409.1570.pdf\" rel=\"nofollow nore... | Is the wavefunction a real physical wave or only a mathematical abstraction? | physics | 2017-05-17T19:45:44.217 |
[
{
"message": "Ive been looking at experiments to look at the IV relationship for a LED, but I see most of them use a rheostat instead of a series variable resistor and my question is, what is the advantage of using a rheostat over a variable resistor in this case?<a href=\"https://i.stack.imgur.com/DIDM5.png\" ... | Diode IV experiment | physics | 2017-05-18T09:39:36.153 |
[
{
"message": "Can both Lagrangian and Hamiltonian formalisms lead to different solutions?I have a simple system described by the Lagrangian\\begin{equation}L(\\eta,\\dot{\\eta},\\theta,\\dot{\\theta})=\\eta\\dot{\\theta}+2\\theta^2.\\end{equation}The equations of motion are obtained from Euler-Lagrange eq.:\\be... | Inconsistency in Lagrangian vs Hamiltonian formalism? | physics | 2017-05-18T13:01:25.000 |
[
{
"message": "Suppose object X is hidden somewhere on Earth and can, somehow, produce \"weak\" gravitational waves, that do not cause anything perceivable by people, but can be detected by all gravitational wave sensors on Earth. (I understand it's impossible due to mass issues, but just suppose it happened by ... | Hypothetical - If a gravitational wave was somehow produced on Earth, could its origin be triangulated? | physics | 2017-05-18T15:05:40.280 |
[
{
"message": "Consider two cosinusoidal signals given by \\begin{gather*} z_1(t) = A_1\\cos\\phi_1(t)\\\\ z_2(t) = A_2\\cos\\phi_2(t) \\end{gather*}with\\begin{gather*} \\phi_1(t) = (\\omega_1 t + \\theta_1)\\\\\\phi_2(t) = (\\omega_2 t + \\theta_2) \\end{gather*}where $\\theta$ is the phase shift of the signa... | Phase Locking vs. Synchrony | physics | 2017-05-18T17:46:38.077 |
[
{
"message": "I have this homework problem in my book, it says:<blockquote> In the circuit shown in the figure, the current flows in the circuit is 0.644A and the the RMS of the AC source is 100V, calculate the reading of the voltmeter.</blockquote>Here is the figure and my attempt to solve the problem, I had ... | Deteminining the voltage across an AC source | physics | 2017-05-18T20:07:47.030 |
[
{
"message": "I'm working a problem from Taylor's Classical Mechanics Book, and it's highlighted a couple issues I never quite wrapped my head around (despite getting good marks in advanced undergrad mechanics and EM).Here are the questions:<blockquote> a) Show that a spring obeying Hooke's Law has a correspon... | Hanging mass from spring/ Setting potential to 0 | physics | 2017-05-18T20:34:46.517 |
[
{
"message": "The Fourier transform of the Dirac distribution is given by$$\\tilde \\delta(\\vec{k}) = \\frac{1}{(\\sqrt{2 \\pi})^3} \\int_{\\Bbb R^3} \\delta(\\vec{r})e^{-i \\vec{k} \\vec{r}} d^3r = \\frac{1}{(\\sqrt{2 \\pi})^3}\\tag{1}.$$By transforming back again, we get an integral representation of the Dir... | Integral representation of Dirac distribution | physics | 2017-05-18T21:32:33.767 |
[
{
"message": "In the course of electrostatics I have come across a basic condition to hold the superposition principle for electric fields, and that is the electric field of one charge should not affect the field of others, that is the first criterion, may be the charges should be placed a minimum distance ap... | Does the limit from a finite to a point dipole violate the superposition principle? | physics | 2017-05-19T22:59:00.950 |
[
{
"message": "Today in our Physics class, we learned about static equilibrium of solid rigid. The teacher presented us with an example in which a man was walking up an inclined board held up by the ground on one end and by his truck on the other (I hope this picture makes sense). At any given moment, the teach... | What is the force a man exerts on a ramp in equilibrium? | physics | 2017-05-20T06:09:28.037 |
[
{
"message": "In these previous questions (<a href=\"https://physics.stackexchange.com/questions/333596/lorentz-contraction-and-magnetism\">Lorentz contraction and magnetism), in order to understand how Lorentz contraction works, I was suggested to first understand “the Bell’s paradox”. But I found the reasonin... | How do different reference frames give different results (such as in Bell's Paradox)? | physics | 2017-05-20T14:07:30.087 |
[
{
"message": "As long as I tried to find out what the total positive amount of energy is in the universe, the only answer I got was 'the total energy in the universe zero', which I do appreciate, but that's not what I am looking for. My question is: what is the total approximated amount of positive energy, in a... | Total positive energy in the (observable) universe | physics | 2017-05-20T17:47:28.867 |
[
{
"message": "In the technique of radio magneto tellurics (RMT), plane wave EM radiation incident upon Earth's surface is used to measure subsurface properties. I have read a number of different sources on the technique. Essentially, Maxwell's equations couple the electric field amplitude and magnetic field amp... | Radio Magneto Tellurics: role of reflection | physics | 2017-05-20T23:18:49.520 |
[
{
"message": "My model is the following: I have a 1D-lattice with L sites. Each site can be occupied by either one or zero atoms. The Hamiltonian looks as follows: $$H = T\\sum(b^\\dagger_i b_{i+1} + h.c.) + V\\sum n_i n_{i+1}$$My question is now of a rather basic quantum mechanical nature. I want to make sure ... | How to make use of a diagonal Hamiltonian for calculating expectation value | physics | 2017-05-21T09:41:27.120 |
[
{
"message": "<a href=\"http://pmt.physicsandmathstutor.com/download/Physics/A-level/Past-Papers/AQA/AS-Paper-1/June%202016%20QP%20-%20Paper%201%20AQA%20Physics%20AS-level.pdf\" rel=\"nofollow noreferrer\">http://pmt.physicsandmathstutor.com/download/Physics/A-level/Past-Papers/AQA/AS-Paper-1/June%202016%20QP%2... | What happens when a voltmeter is connected across two parallel circuits? | physics | 2017-05-21T19:37:26.230 |
[
{
"message": "Light is a electromagnetic wave and its wavelengths determines the colour of the light, so that would be the Hue.<a href=\"https://i.stack.imgur.com/MP8Pl.jpg\" rel=\"nofollow noreferrer\">But what determines the Saturation. The less saturated a colour is the more greyish it becomes. How would you... | How is Hue, Saturation and Brightness of colours explained via EM and QED? | physics | 2017-05-22T13:53:05.190 |
[
{
"message": "I have come across two statements of Noether's theorem which are given below:<blockquote> Statement 1 For every continuous symmetry of the Lagrangian there is a conserved quantity. Statement 2 If the Lagrangian is invariant under the transformation $\\vec q\\rightarrow \\vec q+\\epsilo... | Two statments of Noether's Theorem - do they imply one another? | physics | 2017-05-22T14:23:56.127 |
[
{
"message": "I have two transparent bottles of nearly the same base diameter and cap diameter (Implying that both bottles have similar cap and base area respectively). But one is taller than the other by 15 cm. The bottles are made of the same material (PolyPet) and I poured cold water at the same temperature ... | Which bottle will cool down faster? | physics | 2017-05-23T15:39:52.073 |
[
{
"message": "I'm studying Plasma Astrophysics and now I have came across the following problem, which I have been trying to solve on my own, and came to a \"non-logical\" conclusion?Here is the Problem:Let the Coronal Loop have the following Magnetic Field: $$ B_{x} = B_o e^{-kz}cos(kx)$$ and $$ B_z = -B_o e^{... | Is there any Electric Current on (Solar) Coronal Loops? | physics | 2017-05-23T19:04:55.190 |
[
{
"message": "I know that the line of force at any point in electric field is tangent to the field there however how can I quantitatively find it? As an example if the electric field in a region is given by $\\vec E=x\\hat i+y\\hat j$ how can I find the equation of line of force?",
"role": "user"
},
{
... | How to find the lines of force from electric field? | physics | 2017-05-24T04:07:44.800 |
[
{
"message": "Consider a ship in space that is attempting to stealthily travel between two locations. I hypothesize that it could use the collapse of a wavefunction to tell if it's been detected by using a particle like an electron that would begin in a superposed state and be exposed to the space outside. If... | Could the collapse of a wave function be used to determine whether an object has been detected? | physics | 2017-05-24T05:20:19.257 |
[
{
"message": "Searching for clear explanations of why FTL equals time travel I found this <a href=\"http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel\" rel=\"nofollow noreferrer\">http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travelGo at the bottom, when he draws the blue li... | Help me understand this example about FTL = time travel | physics | 2017-05-24T08:43:20.753 |
[
{
"message": "In general, <a href=\"https://en.wikipedia.org/wiki/Soliton\" rel=\"nofollow noreferrer\">solitons are single-crest waves which travel at constant speed and don't loose their shape (due to their non-dispersivity), and there are many examples of them in the real world. Now in QFT a soliton can be d... | Do solitons in QFT really exist? | physics | 2017-05-24T09:49:45.047 |
[
{
"message": "I'm teaching myself about QM, but there are something really puzzling me about the simple harmonic oscillator:$$H=\\frac{p^2}{2m}+\\frac{m\\omega^2x^2}{2}.$$I've learned how to use ladder operators to obtain the eigenvalues of this oscillator. Also, I'm able to write out the eigenstates in the for... | How many wave functions can be represented as a superposition in a simple harmonic oscillator? | physics | 2017-05-24T11:07:24.017 |
[
{
"message": "How can I calculate the mean kinetic energy of an emitted neutron in a nuclear fission. Take for example the fission of U-235 to Ba-141 and Kr-92. A calculation which just shows that the mean energy will be in the range of \"fast\" neutrons (> 1MeV) would be enough for me.",
"role": "user"
}... | Calculate kinetic energy of neutrons in nuclear fission | physics | 2017-05-24T13:00:58.520 |
[
{
"message": "Will field at plane of a disk excluding the disk itself be zero? Here basis of above conclusion is that the field lines will originate perpendicularly to the plane, and from both faces therefore they will never be able to reach plane of disk at finite distance.From above the potential at edge will... | Electric field at plane of non-conducting uniformly charged thin disk | physics | 2017-05-24T14:56:59.187 |
[
{
"message": "I get that the gravitational pseudotensor is generally only used for asymptotically flat spaces (aka quasi-Minkowski). In these cases, conserved total energy momenta can often be found for some system (and the various pseudotensors out there tend to agree with one another).I recently came across W... | Using the gravitational pseudotensor on a finite space | physics | 2017-05-24T22:52:15.680 |
[
{
"message": "What happens when two or more independent heat sources heat the same object?For example, where one heat source on its own creates an equilibrium temperature with the object of 35C, and the other creates an equilibrium temperature with the object at 50C - also on its own.Assume the same object area... | Muliple heat sources, same object - final temperature reasoning | physics | 2017-05-25T02:32:01.990 |
[
{
"message": "I was reading the post <a href=\"https://physics.stackexchange.com/q/141331/\">Which dissipates more power, a small or big resistor? and DanielSank's reply said<blockquote> Now, any circuit you would reasonably call a \"voltage source\" must have a low internal resistance compared to typical loa... | Resistance in internal battery, voltage source | physics | 2017-05-25T02:48:25.563 |
[
{
"message": "There is the standard definitive statement of the conservation of energy momentum:$$\\nabla_{\\mu}T^{\\mu\\nu}=0$$Which one expects to be upheld everywhere on some spacetime region M i.e four-volume (covariant divergence if not flat).$$\\intop_{M}\\nabla_{\\mu}T^{\\mu\\nu}dM=0$$ This has been show... | Valid Argument for total energy of a closed universe to be zero? | physics | 2017-05-25T04:25:56.337 |
[
{
"message": "My question is what are the steps for taking an integral of the following form?$$\\int e^{-\\alpha|\\mathbf r- \\mathbf R_a|^2} {1\\over|\\mathbf r- \\mathbf R_b|} e^{-\\beta|\\mathbf r- \\mathbf R_b|^2} dV$$This integral is commonly seen when attempting to do Quantum Chemistry calculations with a... | Evaluating Potential Energy Integral in Quantum Chemical Calculations | physics | 2017-05-25T19:08:47.257 |
[
{
"message": "<a href=\"https://arxiv.org/abs/1404.1207\" rel=\"nofollow noreferrer\">https://arxiv.org/abs/1404.1207I have some questions in regard to this paper. If I am not mistaken it is akin to Alexander Vilenkin's proposed cosmological model that has the Universe begin to exist from a quantum nucleation e... | What is meant by "spontaneous creation" in this paper? | physics | 2017-05-25T19:40:26.387 |
[
{
"message": "Polonium-210 was used to murder Alexander Litvinenko in London in 2006. That dose was estimated to cost $8m and had to be created in a nuclear reactor. A tiny dose of it was incredibly deadly.I'm a high school physics teacher and we use polonium-210 as an example of an alpha source in class. It co... | What is the difference between polonium-210 in my school lab and polonium-210 used to kill Alexander Litvinenko? | physics | 2017-05-25T19:51:14.983 |
[
{
"message": "Please note that I just read about 20 forum discussions, none of which answered my question. This question is related to my earlier question <a href=\"https://physics.stackexchange.com/q/297697/\">Is spacetime symmetry a gauge symmetry?.I am looking for a definition of <a href=\"https://en.wikiped... | What is a gauge theory? | physics | 2017-05-25T21:10:55.190 |
[
{
"message": "The energy momentum tensor for a perfect fluid is defined as: $T^{\\mu \\nu} = (\\rho + p)U^\\mu U^\\nu + p \\eta^{\\mu \\nu}$Where $\\rho$ is the energy density, $p$ is momentum, $U$ is the four-velocity (tangent vector parameterized by proper time), and $\\eta$ is the Minkowski metric.I've read:... | Questions regarding projecting the energy momentum tensor for perfect fluid along the four-velocity | physics | 2017-05-26T02:15:49.497 |
[
{
"message": "Suppose, a block of mass $m$ hangs from a spring of negligible mass and force constant $k$. I had to find the equilibrium position of the block. [i.e how long is the spring stretched at equilibrium]. <a href=\"https://i.stack.imgur.com/33559.gif\" rel=\"nofollow noreferrer\">Basically, I have to f... | Paradox in simple homework problem | physics | 2017-05-26T04:25:18.607 |
[
{
"message": "How is the conclusion that the Higgs quartic coupling becomes negative at high energies ($\\sim 10^{10}$) GeV inferred? I'm looking for a reference that has the necessary idea and calculations to understand this.What does this instability of Higgs potential at such energies imply at a conceptual l... | Understanding how the quartic Higgs coupling turns negative at high energies | physics | 2017-05-26T09:34:51.497 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.