All Questions

0
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0answers
4 views

Stellar aberration: distal or local? Experimental proof?

Stokes put forward the theory (I am simplifying here.) that stellar aberration takes place out in space and that light from stars is already fixed in direction with respect to the Earth's surface by ...
0
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0answers
4 views

Could a material be created to effectively negate directed energy weapons?

You always see lasers and plasma guns being used in SF space battles, but couldn't a sufficiently reflective or absorbent material be utilized to essentially make these sorts of weapons useless? On ...
0
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0answers
3 views

Does bending a piece of steel change the speed of sound in it?

Specifically, I have a student investigating sound produced in a helical spring (slinky) when struck. When it is struck it produces a sound that changes in pitch - from very high to quite low. Also, a ...
-6
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0answers
33 views

Is quantum mechanics misleading [on hold]

Mechanics implies dynamics. Yet all of the qm I have seen is empirical curve fitting of a static system. Maybe they should change the name? For example it seems the point of qm is to do an experiment,...
0
votes
1answer
14 views

Motion of the center of mass of rigid bodies in space

For the classic two body problem, I know that the motion of the center of mass is a straight line (with respect to an inertial frame), provided that the bodies are considered as point particles. Now ...
0
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0answers
16 views

Sound wave equation: Neumann boundary conditions

In this paper it's described the solution of the damped wave equation in cylindrical coordinates $$ \nabla^2\left(c^2\rho_1+\nu\frac{\partial\rho_1}{\partial t}\right)-\frac{\partial^2\rho_1}{\...
-2
votes
0answers
21 views

Orbit velocity satellite question, is this question ill defined [on hold]

I am attempting to solve this question but I feel that the question may be ill defined. The question is in two images, the first image and second image. I have tried many attempts at this. The ...
-1
votes
1answer
21 views

Equivalent resistance in triangle

How do I find equivalent resistance between A and B? I'm not sure which resistors to connect, and how, parallel or in series.
0
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0answers
8 views

Design of quarter wave impedance transformer from waveguide

Assuming air filled waveguide with transformer section having same width as that of the input and output sections , what should be the height and length of a single section quarter wave impedance ...
1
vote
1answer
48 views

Rigorous definition of generalized coordinates

In Goldstein's classical mechanics and in many other books I haven't seen a rigorous definition of generalized coordinates. In a system of $N$ particles described by $\textbf{r}_1, \dots, \textbf{r}...
0
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0answers
24 views

Cartesian basis vectors in polar coordinates

I'm trying to solve a problem which includes a spinning object and I want to find it's velocity vector with respect to an object moving in a straight line on the the x axis with constant velocity. I ...
0
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0answers
16 views

Speed of an object when moved by two belts

There is a transport drive with a top belt driven by a motor M1 and a bottom belt driven by a motor M2. Between the belts there is an object which borders with each of the belts equally and due to ...
0
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0answers
10 views

By how much does space-time curvature modify the density of an object?

Let's imagine a transparent object with a density $\rho_0$ [$kg/m^3$] (A sphere of glass as example). Now I send through this object a long flat impulse of electromagnetic plane wave with frequency $\...
0
votes
1answer
22 views

How exactly does does friction rotate a wheel?

All I know is that the wheel pushes the ground and the ground pushes back (friction). Pls can anyone elaborate on this process?
0
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0answers
11 views

Solution of the diffusion equation in a plasma

considering the diffusion equation taking into account diffusion and mobility of charged particules in a plasma of density $n(z)$ and potential $\phi(z)$, we have : $$ \frac{n(z)}{\tau}=\frac{\...
0
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0answers
6 views

Can Matrix Product States be used to describe ergodic states?

The eigenstates in the ergodic phase of the disordered interacting quantum many-body system follow a volume law of entanglement. Since MPS follows area law, can we use any MPS based algorithm (ITEBD ...
2
votes
0answers
14 views

Eddy Currents and magnet's orientation with respect to motion

I am doing a report on an experiment on harmonic oscillators. We added magnets to the cart (they move with it) to provide magnetic dampening, placing the magnets once horizontally and once vertically (...
0
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0answers
18 views

HELP in particle physics [on hold]

How to calculate the differential cross section for bhabha scattering in the center of mass system? and as a function of cos(theta)?
0
votes
1answer
22 views

Hyperfine structure of hydrogen

I have an expression $H=a \vec{I} \vec{S}$ which is a leading term in Hamiltonian for the hyperfine structure of p-states in hydrogen, but I don't really understand it. By Wigner-Eckart, hyperfine ...
0
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0answers
37 views

How to indicate this formula with nabla operator? [migrated]

I found this in the fluid mechanics: $F(u)=\frac{\partial u_x}{\partial x}\frac{\partial u_y}{\partial y}+\frac{\partial u_x}{\partial x}\frac{\partial u_z}{\partial z}+\frac{\partial u_y}{\partial y}\...
0
votes
0answers
10 views

Solenoid and circular loop, mutual inductance

I have to solve this physics problem: Consider a solenoid with N turns per unit of length and a circular loop, both of radius a. These, are placed one after the other, in a coaxial form, separated a ...
1
vote
0answers
43 views

Lecture notes by Rudolf Mössbauer

Rudolf Mössbauer was an excellent lecturer. He gave lectures on Neutrino Physics, Neutrino Oscillations, The Unification of the Electromagnetic and Weak Interactions and The Interaction of Photons and ...
0
votes
2answers
34 views

Collision & Work

Let's assume there is an unusual guy and whenever he is shot, the bullets actually jump off of him towards the opposite direction, in the x-axis. I need to find the work applied by the guy per minute ...
4
votes
0answers
24 views

Do longitudinal and scalar have anything to do with Faddeev-Popov ghosts?

In his this book, Hatfield calls ghosts the negative states appearing in the covariant (Gupta-Bleuler) quantization prescription of the electromagnetic field (page 89). When discussing Yang-Mills ...
3
votes
1answer
42 views

Exact form of the damped wave equation

The undamped wave equation has the standard form \begin{equation*} \frac{\partial^2 \psi}{\partial t^2}=c^2\nabla^2\psi \end{equation*} while the damped wave equation is frequenly found written in ...
1
vote
1answer
29 views

SLAC Energy doubler (SLED)

A method of doubling the energy at the expense of pulse width is what SLED is all about. Could this method be applied to any other accelerator other than the one applied in the paper SLED A method ...
-1
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0answers
21 views

quantum mechanics and calculations for small spacetime regions

What is your position on one of Feynman's statements regarding the nature of Quantum Mechanics and the infinite amount of calculations needed to estimate a quantum property of a very small segment of ...
0
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0answers
30 views

What can be done to find the angle $\theta$ of the prism?

Below there's an illustrated diagram Consider that a parallel beam of light is incident from air at an angle $\alpha$ on the side PQ of a right angled triangular prism of refractive index $n$. Light ...
0
votes
0answers
10 views

Calculate capacitor discharge amps [on hold]

If I charge a 1uF 2kv capacitor using a 2kv power source until it become full. And then discharge the capacitor. What is the maximum amps do I get when the capacitor discharge? Edit: Do I missing R (...
4
votes
1answer
55 views

How is pressure calculated in the early universe?

I'm trying to calculate the sound horizon from the start of time to decoupling. To do this I need to know the speed of sound and how it changes as the universe grows. The speed of sound in a fluid ...
1
vote
2answers
69 views

Implementing a spherical pendulum

I am trying to implement a spherical pendulum. The Lagrangian (which I haven't fully understood so yet) based on $l$, θ and φ taken from this page result in the equations: \begin{align} \...
4
votes
1answer
47 views

What would happen if we had a crystal structure but only gravitational interactions?

The idea is simple. Let's say we arrange similar bodies (call them planets, ions, anything) in an infinite crystal structure, but the only possible interactions are gravitational interactions. A ...
0
votes
0answers
26 views

Expectation values of states in QFT via the path integral

The path integral in QFT is usually computed only for the vacuum state, $$\langle 0 | T\{ A \} | 0 \rangle = \int \mathcal{D}\phi(x) A e^{iS[\phi]}$$ Doing it for different states is a bit trickier,...
2
votes
0answers
26 views

How to prove that the Lorentz connection corresponding to tetrad formalism is super covariant?

given the tetrad formalism: $\nabla_{\mu} e_{\nu}^{a}(e)=\partial_{\mu}e^{a}_{\nu}+\omega_{\mu b}^{a} e^{b}_{\nu}-\Gamma^{\sigma}_{\mu \nu} e^{a}_{\sigma}$ show that $ \hat{\omega}_{\mu}^{ab}=\omega_{\...
0
votes
0answers
21 views

Why is the different p.d. same across different resistors in series connection? [on hold]

The total potential difference in a circuit is said to be equal to the total potential drops, why? The energy is lost as heat and the potential drops are always lower than the potential difference so ...
0
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0answers
8 views

Timescales of plasma recombination and fluorescence?

I am currently working on a very simple model for the radiation from electric arcs. As both fluorescence (internal electronic transition) and plasma recombination occur, I would like to compare the ...
0
votes
1answer
63 views

Physics mystery : why does it rotate?

In the beginning this thing was floating still and the candle was out. Then someone lit the candle and the flame somehow Made the object spin on the water. See the picture. I know a little bit about ...
0
votes
0answers
14 views

Electric field lines in a two point charge conducting surface [on hold]

The magnitude of E at the surface of an irregularly shaped solid conductor must be greatest in regions where the surface curves most sharply, such as point A and must be least in flat regions such as ...
0
votes
0answers
22 views

$y$-component and $z$-component not equal to zero

If we were to place a point on the perpendicular bisector of an evenly charged rod of positive charge, lying along the y-axis, By symmetry are there any other ways that the electric field's y and z ...
-3
votes
1answer
26 views

Bose Einstein Condensate

In Bose Einstein condensate photons stop moving, but with reference to what frame of reference? Photons move at constant speed in all reference frames so what happens to Maxwell equations at zero ...
0
votes
1answer
30 views

C and T Symmetry of Free Dirac Lagrangian

I want to show the $C$ and $T$ symmetry of the free Dirac Lagrangian $$\mathcal{L}=\overline{\psi}\left(i\gamma^\mu\partial_\mu-m\right)\psi.$$ Following the notation of Peskin, Schroeder, we have ...
2
votes
1answer
25 views

What the difference is between Størmer Verlet and regular Verlet method?

I was wondering what the difference is between the Størmer Verlet method and the regular Verlet method, if there is any.
0
votes
2answers
70 views

What's wrong with this mechanics question? [on hold]

Just working through a question and I don't think it's possible to solve without more information. Am I right or am I missing something? A 66 kg ice skater comes to rest uniformly on rough ice from ...
2
votes
1answer
45 views

Getting the density of states for photons

I know that the density of states $g(\epsilon)d\epsilon$ is the number of states in the energy range $[\epsilon, \epsilon + d\epsilon]$. I considered a system of non-interacting free photons in 3 ...
3
votes
3answers
92 views

Having trouble making sense of Einstein's thought experiment

So I was reading about Einstein's thought experiment where he tries to show that simultaneous events in one frame may not be simultaneous in another frame. So, in the given pic, light from B' ...
0
votes
0answers
36 views

Necessary condition for Entropy to be a state function

In a thermodynamic process, entropy change from a state $a$ to $b$ is defined as $$ \int_{a}^{b}\frac{\delta Q_{rev}}{T} $$ But, there can be infinitely many reversible paths to reach $b$ from $a$. ...
1
vote
1answer
26 views

What exactly is the time step in weather predictions?

The question basically says it all. I am confused as to what the 'time step' in weather prediction signifies-- is it the time interval between each measurement of the initial condition? Or is it the ...
0
votes
0answers
38 views

Why is force defined the way it is? [duplicate]

In classical mechanics an inertial frame is a frame of reference where: $\vec{F}=m\frac{\mathrm{d^2}\vec{x}}{\mathrm{d}t^2}$ holds. Couldn't we have expanded this set of inertial frames of reference ...
0
votes
1answer
27 views

Metropolis Monte Carlo Phase Transition for small systems

Metropolis Monte Carlo simulation for the argon liquid fails to reproduce correctly the pressure-temperature isotherm from the point of liquid-vapour coexistence: Why such a phenomenon appears ? The ...
0
votes
0answers
10 views

What is the definition of pitch of a helix (spring) in terms of slope?

This question is linked to another question that I asked in Math section. I think this specific part is more relevant to physics. I have designed a 3D helix structure. The radius is constant but the ...

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