Newest Questions
244,124 questions
13
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Is there a rigorous equivalence between the ball-on-hemisphere and falling rod problems?
These are two well-known problems in classical mechanics that yield the same critical result:
Problem 1: Ball on a Hemisphere
A small ball of mass $m$ is placed at the top of a smooth (frictionless) ...
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1
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0
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27
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Specular Reflection for Transparent Materials
I’ve been wondering what would happen if I used a laser of a different wavelength for specular reflection on glass surfaces. Would a shorter, or longer, wavelength give stronger reflection or higher ...
- 31
0
votes
1
answer
46
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How electron recieves energy from electromagnetic wave? [duplicate]
I know that if I oscillate an electron, it will produce electromagnetic wave, the energy I use to oscillate the electron is radiated as electromagnetic wave. But if an electron is kept in front of an ...
- 290
2
votes
1
answer
68
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Why does an angular velocity vector have an "expressed-in" frame?
$\newcommand\p[3]{{}^{#1}{p}^{#2}_{#3}} \newcommand\pdot[3]{{}^{#1}{\dot{p}}^{#2}_{#3}} \newcommand\pddot[3]{{}^{#1}{\ddot{p}}^{#2}_{#3}} \newcommand\R[2]{{}^{#1}{R}^{#2}} \newcommand\Rdot[2]{{}^{#1}{\...
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6
votes
1
answer
67
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Soft graviton theorem and derivatives of the dirac $\delta$ function with respect to the hard momenta
I am reading the paper titled Testing Subleading Multiple Soft Graviton Theorem for CHY Prescription. In the text corresponding to eqs. (3.1) through (3.7), the authors justify why
$$\sum_{a=1}^n\frac{...
- 4,325
2
votes
1
answer
98
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Why can we shift the renormalization scale in the RG flow?
It seems that the most natural way of choosing renormalization scale is to separate Lagrangian into physical Lagrangian and counterterms , like in Peskin & Schroeder's book, chapter 10.2, p.325, ...
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0
votes
0
answers
44
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QED replacing photon field with current in 3-point function
I am self-studying QFT in the Schwartz book "Quantum Field Theory and the Standard Model", currently I am struggling to understand the all-orders proof that $Z_1=Z_2$ using Ward-Takahashi ...
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4
votes
1
answer
174
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Angular acceleration about different axes
Say you have a wheel floating in space with forces of equal magnitude acting upward at the COM and downward at the right edge. I have always been under the impression that no matter the inertial frame ...
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2
votes
2
answers
62
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Let $\rho_0(x,y,z,t)$ be the initial mass density field then could we calculate its evolution with time using newtonian mechanics and how? [closed]
I've been trying to find a way to make this work but the only thing I have gotten to is that the integral of the mass density over space is equal to the total mass.
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3
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0
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39
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In Newton-Cartan spacetime, can we write down the absolute time condition $(d\tau = 0)$ in terms of the temporal metric $t_{\mu\nu}$?
Typically, a Newton-Cartan spacetime is defined as a $d$-dimensional manifold $M$ along with
A degenerate symmetric contravariant degree-2 tensor $h^{\mu\nu}$ called the spatial metric.
A nowhere ...
- 2,017
0
votes
2
answers
129
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How can water with a very tiny change in density increase the pressure so much?
We have two tanks full of water, one is 1bar second is at 100bar.
In both tanks water has same density(tiny difference) and temperature, that mean same number of molecules(almost the same) at the ...
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0
votes
0
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22
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BRST anticommutation relation and Virasoro generators [closed]
I have been bothered for couple days by how to derive (3.2.19) in Green, Schwarz, Witten's book <Superstring Theory volume 1>.
The formula is
$$Q^2=\frac{1}{2}\{Q,Q\}=\displaystyle\frac{1}{2}\...
-3
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0
answers
75
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does a neutrino really a massful particle? [closed]
neutrinos mass problem ?
generally neutrinos mass problem became more terrific to me because as i studied in my class text books a neutrino is a particle which is either released in some decays and my ...
3
votes
1
answer
423
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The problem of the perfectly horizontal string
Suppose we have a piece of string, of non-zero mass, whose two ends are attached to two heavy blocks, where the two points of attachment have the same height measured from the ground.
In other words, ...
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-1
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4
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374
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When the frequency ceases to exist
As long as a frequency has a wavelength and an amplitude, it can be called a frequency.
If I look to the anatomy of a frequency, what happens if a frequency transforms to a wavelength reduced to 0? Or,...
