Questions tagged [physics]

Questions on the mathematics required to solve problems in physics. For questions from the field of mathematical physics use (mathematical-physics) tag instead.

This tag is for questions on the mathematics required to solve problems in physics and should not be confused with those on physics concepts. Pure physics questions should go in the Physics Stack Exchange. For questions in the field of mathematical physics, please use the tag instead.

5372 questions
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What will be the form of the equation of a standing wave in circular form as shown below?

Following is the image of a 3D standing electron wave in circular form. Each of its loop moves up and down (while the adjacent loop is supposed to be $\pi$ radians out of phase) i.e. out of the plane and also into the plane. I think the wave…
user400242
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How to evaluate the Jacobian of an arbitrary spacetime transformation?

Under a Poincare transformation $$x^{\prime\mu}=x^\mu+\delta x^\mu=\Lambda^{\mu}{}_{\nu}x^\nu+\epsilon^\mu.\tag{1}$$ where first term corresponds to an arbitrary Lorentz transformation and the second term represents a translation in spacetime. I'm…
SRS
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Derivation of fluid Power due to Shear stress and normal stress

How can it be shown that the (i) power component of a fluid due to shear stress $S_\tau$ $\dot{W}_{s_\tau} = -2\mu\int_A e_n \cdot (\vec{V} \cdot \dot{S}) dA + 2\mu \int_{\forall} (\dot{S} \cdot \nabla)\vec{V} \: d\forall$ (ii) and power…
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Noether's Theorem proof

Here is the proof of Noether's Theorem given in Peskin's and Schroeder's book on QFT: What I don't understand is why he writes that $\Delta \mathcal{L} = \frac{\partial\mathcal{L}}{\partial\phi}\Delta\phi +…
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The integral under the variation $\delta$ sign

In physics books on classical field theory, the authors usually define the action as $$ S = \int\mathcal{L(\phi,\partial_\mu\phi)d^4x} $$ where $\mathcal{L}$ is the lagrangian density. Then, they say that the principle of least action states…
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What's wrong in this "counterexample" of the Moyal´s product associativity?

I have been working in the phase space formulation of quantum mechanics, and stumbled upon the following problem: Consider the phase space functions : $e^{ip\epsilon /\hbar}$, $e^{-ip\epsilon /\hbar}$ and $W(x,p)$, where $e^{\pm ip\epsilon…
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Degree of Divergence of connected Feynman digrams

Background: Consider a connected Feynman diagram $\Gamma$ with $E$ external lines, $I$ internal lines, $L$ loops and $V$ vertices in dimension $D \in \mathbb N$. If you are unfamiliar with the physicist's language, please consult Diagramology by Tim…
Nanashi No Gombe
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How can eigenvectors of a Hermitian matrix be entangled?

This question comes from physics, but I will reduce the amount of physics jargon. You have a tensor product space $H_1 \otimes H_2$. Any vector $w$ in this space has a Schmidt decomposition: $$ \mathbf{w} = \sum_{i} \alpha_i…
DLV
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Prove $v = \sqrt{\frac{2gRh}{R + h}}$ from Given (below)

Given: $$F = \frac{mgR^2}{(x + R)^2}$$ $m = \text{mass}$ $g = \text{Acceleration due to gravity}$ $x = x(t)$ is the object's distance above the surface at time $t$. I believe this is the Universal Law of Gravitation (correct me if I am wrong) Also…
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Viscous Burgers' equation with a coefficient to the nonlinear term

I am considering the following PDE \begin{equation} u_t + \alpha \, u u_x - \beta \, u_{xx} = 0 \end{equation} with $\alpha, \beta > 0$. When $\alpha = 1$, this is the viscous Burgers' equation. Given a solution for a case with $\alpha = 1$, I would…
XavierStuvw
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Basic Physics question

Velocity vector $A$ has components $A_x=3 \text{ m/s}$ and $A_y=4 \text{ m/s}$. A second velocity vector $B$ has a magnitude that is twice that of $A$ and is pointed down the negative $x$-axis. Find the $x$ component of $B$ This is what I…
Zoey
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Physics related antiderivatives problem

I was wondering if I could get a little help with a calculus related word problem: A car braked with a constant deceleration of 5 meters per second squared for 60 meters before stopping. How fast was the car traveling when the brakes were applied? I…
Alis
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Need help understanding a particular proof regarding integration to find the net electric field

I have the following question regarding Electromagnetism. I have placed the question here instead of Physics Stack exchange since it is specifically the mathematics and not the physics concepts that I am questioning here: I actually have the…
BLAZE
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Tension of Each Half (Using Vectors)

A clothesline is tied between two poles, 8m apart. The line is quite taut and has negligible sag. When a wet shirt with a mass of 0.8kg is hung at the middle of the line, the midpoint is pulled down 8cm. Find the tension in each half of the…
mathguy
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Finding Height In Gerstner Wave Function In World space.

Using the GPU Gems Article Effective Water Simulation From Physical Models I have implemented Gerstner Waves into UE4, I have built the function both on GPU for the tessellated mesh displacement and in code for the purpose of sampling height of the…
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