2
votes
1answer
104 views

Why is the inertia ellipsoid of a higher symmetry than the rigid body?

I was always puzzled by this fact. A uniform cube has a sphere-shaped inertia ellipsoid. The sphere has a higher symmetry then the cube. Is there any deep reason or implication behind it?
-2
votes
0answers
24 views

problem: polarized sphere [on hold]

Need some help with a practice exam question: Given a solid sphere with radius R, with polarization density given by $P(\vec{r})) = a(R-r) \hat{z}$ . I need to find the potential inside the sphere, ...
1
vote
1answer
40 views

What force counteracts friction when a block is pulled?

Firstly, I understand and apologize that this is more of a physics question than a math question. I noticed that when I pulled a book out from under a pack of gum, the gum stayed largely in place (it ...
-1
votes
0answers
19 views

Preventing a train from derailing during turning by applying breaks from back to front [on hold]

My understanding regarding the derailing of trains during turning is that it occurs due to brakes being applied, from front to back, before the full length of the train has completed the turn which ...
4
votes
1answer
127 views

Does any lower frequency electromagnetic radiation naturally reach us from the Sun?

I am not sure whether the sun originally emits everything in the electromagnetic spectrum, (whatever the relative strengths of each portion might be), but I do read that many waves, including gamma / ...
-1
votes
0answers
24 views

Trying to calculate the average speed from this question [on hold]

I already checked the average speed question that was posted before and tried applying the methods to my question but nothing seemed to work. I would like to know if anyone can explain to me how to ...
-1
votes
3answers
65 views

Differences between wavefunction, probability and probability density?

I am trying to understand the differences between wavefunction, probability and probability density. There are different definitions on the internet. For example: ...
2
votes
2answers
81 views

Interpretation of a density matrix as an observable

In quantum mechanics, any density matrix (or density operator) is Hermitian. Observables are also represented by Hermitian operators. So it follows that a density matrix can also be interpreted as ...
2
votes
2answers
60 views

First-order and second-order wave equations, versus the uncertainty principle

In classical physics, we have second-order equations like Newton's laws, so we need to specify both position (zeroth order) and velocity (first order) of a particle as initial conditions, in order to ...
0
votes
0answers
16 views

Heat engine efficiency, compression ratio vs temperatures

I want to understand the role or even existence of a cold reservoir in the Otto cycle gasoline engine. The efficiency of the Otto engine is given as a function of compression ratio $$ ...
20
votes
3answers
1k views

The physical definition of work seems paradoxical

So this is possibly a misunderstanding of the meaning of work, but all the Physics texts, sites, and wiki that I've read don't clear this up for me: In the simplest case with the simplest statement, ...
-3
votes
0answers
39 views

What are quasars?

I was taught that apart from stars, the other self illuminating objects in the universe are quasars. What are quasars? It seems the definition of a quasar is an active galaxy? What is that and how ...
0
votes
0answers
19 views

Is it possible to go to graduate school in physics with a different undergrad degree? [on hold]

Specifically, a major in mathematics or applied math, while self studying the undergraduate physics curriculum, as I also want to major in computational biology. A triple major would make it difficult ...
1
vote
1answer
84 views

Why does a minor vertical vibration cause my coffee to spill?

When I walk my kid sometimes I put a cut of coffee in a cupholder attached to the stroller. When I push the stroller over a brick pavement it seems to vibrate vertically. That is enough for the coffee ...
1
vote
2answers
81 views

Action and Action integral: Different kinds of variational principles

What are the difference between: the action $\int_{t_{1}}^{t_{2}}(L+H) dt$ that we use in the principle of least action, and the action integral $\int_{t_{1}}^{t_{2}}L dt$ that we use in ...
1
vote
3answers
53 views

Basics of Current Electricity

I have certain questions which confuse me a great deal. I want to have a very basic and clear idea about some concepts. Here it goes: 1) I am really confused on how a battery actually works. The very ...
3
votes
0answers
46 views

Introductory derivations of Heisenberg uncertainty principle

I'm not an expert when it comes to quantum mechanics, so correct me wherever I'm wrong, but: I've always been a little bit bothered by introductory derivations of the Heisenberg uncertainty relations ...
3
votes
2answers
97 views

Why does blowing on hot coffee cool it down?

And will it cool off faster if you blow across the top of the cup or directly into the coffee? Does it have to do with the fact that when you blow across the top of the cup the velocity of the air ...
0
votes
0answers
9 views

How to survive a lightning strike [migrated]

Is this really a plausible way to survive a lightning strike ?
0
votes
0answers
21 views

Calculate Power requred to rotate a certain disk at a specific RPM in different conditions [on hold]

I have two acrylic disks with $x$ radius and $y$ thickness. I want to rotate that disk at certain RPM using a Motor. I know the weight of the disk. the weight of the Disks are virtually uniformly ...
5
votes
1answer
122 views
+50

Coleman-Weinberg potential: resum at 2 loops?

Say we want to compute the Coleman-Weinberg potential at 2 loops. The general strategy as we know is to expand the field $\phi$ around some background classical field $\phi \rightarrow \phi_b + ...
0
votes
0answers
24 views

Polarizable molecule in E-field

If we have a linear molecule with a dipole moment $\mu$ in a static electric field $E$, the potential is given by $V = - \langle \mu,E \rangle$. What is the appropriate equation for the potential if ...
1
vote
0answers
18 views

Energy conversion efficiency of Q-switched laser?

This is kind of an elementary question, but since i cannot find a reliable source on this i wanted to ask what is the formula for energy conversion efficiency? I know efficiency is calculated as ...
-1
votes
0answers
21 views

States that Wave-length, Pressure and Temperature describe [on hold]

I have two doubts : 1 - Can wave-length of light emited by some light-source ( like a black-body ) take arbitrary distance values ( any value in the set of real numbers ) ? 2 - Pressure is the name ...
1
vote
0answers
40 views

Confusion on entropy in the universe [on hold]

I was researching about the heat-death of the universe, and I was wondering if my understanding of it so far is factual to the theory? However, the 3rd Law of Thermodynamics prevents the universe’s ...
2
votes
2answers
38 views

Sound Wave out of phase

I connected my speakers to my sound system switching the +ve and -ve one of the speakers I can notice them beating out of phase but how come I don't hear any difference and at what position will it ...
1
vote
0answers
41 views

Are there any known (closed form even if approximate) solutions to problems in relativistic elasticity?

There are several useful known solutions to the EFE with relatively simple / trivial stress-energy-momentum tensor, such as the Schwarzschild solution. Despite the idealizations made therein they are ...
1
vote
0answers
73 views

Mathematical model that allows the existence of an infinite number of smallest, but different particles

Does there exist a mathematical formalism (model) in particle physics that assumes the existence of an infinite number of different, yet smallest particles (building blocks)?
13
votes
2answers
169 views

Physics of “boing” sound in raquetball courts?

While playing raquetball, I frequently hear a very prominent "boing" sound (or more formally, a chirp). For example, you can hear it in this video when the ball hits the front wall. Does anyone know ...
2
votes
1answer
54 views

Invariance of canonical Hamiltonian equation when adding the total time derivative of a function of $q_i$ and $t$ to the Lagrangian

The following is exercise 8.2 in 3rd edition (and exercise 8.19 in 2nd edition) of Goldstein's Classical Mechanics. Adding the total time derivative of a function of $q_i$ and t to the Lagrangian ...
0
votes
0answers
44 views

Mathematical formalism to include wave and particle perspectives of light

Does the exist any mathematical formalism (model) describing the behavior of light and incorporating its particle character (divisibility, quantization) and wave character? (i.e. quantized wave model) ...
0
votes
1answer
66 views

What exactly is a gauge anomaly?

In lots of papers I read about gauge anomalies. For example, avoiding gauge anamolies in the MSSM is the reason for introducing an extra Higgs doublet. Gauge anamolies in the Standard Model are ...
0
votes
3answers
35 views

Magnetic declination [on hold]

i couldnt just figure out when i got to know that declination can be zero also. How can true and magnetic north ever align themselves in a straight line in any place? Also if a compass aligns in the ...
-1
votes
1answer
14 views

Work to pump water through a hole in a trapezoidal prism

So I don't want to give the full details of the problem I'm working on, since I want to solve it myself. But I'm not sure which physical principles I'm supposed to use, since this is a Calc 2 ...
1
vote
1answer
29 views

Peaks and dips position in the Planck CMB

I am currently looking for the values of the firsts peaks and dips (at least the first 3) in terms of l and angular size for the CMB angular power spectrum measured from Planck. But the only thing I ...
2
votes
3answers
73 views

Is thermodynamic free energy and potential energy the same thing?

The equation for free energy $F$ and potential energy $E_{pot}$ are: $$ F=U-TS \\ E_{pot} = E_{tot} -E_{kin} $$ But the temperature $T$ is proportional to the average kinetic energy of a system. So ...
1
vote
3answers
74 views

Can light be trapped theoretically?

My question is a little silly I know, but I'm curious to know if a particle of light can be theoretically trapped between two reflective screens. For example once the particle of light has left it's ...
6
votes
3answers
273 views

Eigenvalues of the Lagrangian?

It is often stated that the Lagrangian formalism and the Hamiltonian formalism are equivalent. We often hear people talk about eigenvalues of Hamiltonians but I have never ever heard a word about ...
1
vote
0answers
52 views

Ergodic Hypothesis; canonical ensemble

I'm currently studying for an exam in thermodynamics/classic statistical mechanics and 2 things came up which are confusing me. First the ergodic hypothesis states that it is equal to take the mean ...
0
votes
0answers
43 views

Uncertainty principle implies the non-deterministic universe? [duplicate]

Does the uncertainty principle imply the non-deterministic universe, or just the fact that our model of the universe, the one based on observation, can be at most non-deterministic, since we will not ...
4
votes
2answers
465 views

Why are most accurate reflective surfaces not white?

Since white is our perception of reflection of light, why are mirrors and other metallic objects that are more grey or silvery capable more reflective than a white object? This is somewhat related: ...
9
votes
1answer
744 views

Why did nuclear testing not result in nuclear winter?

According to Wikipedia over 2000 nuclear tests have been performed since the Manhattan Project. If nuclear war would bring about a nuclear winter, why didn't testing do? Were they too much spread out ...
0
votes
1answer
40 views

Experiment with spring and two light sources emitting light in opposite directions

Two (almost massless) light sources connected with a (almost massless) spring emit light beams in opposite directions. What is the speed at which the spring extends?
1
vote
0answers
35 views

How strong can tidal forces get?

I am imagining a planet the size of Earth being in close proximity to something of high mass such as a gas giant or a star, but ultimately I'd be more interested in how to figure this out myself. So ...
3
votes
1answer
97 views

What conditions do a bunch of atoms need to satisfy to have a temperature?

Suppose that we have a beam of helium atoms travelling in a common straight line, equally spaced with the same velocity. If we place a thermometer in the path of this beam, the atoms will impinge on ...
0
votes
1answer
22 views

What does the term 'hyperbolic model' mean?

I am reading this non-linear discrete dynamical system paper. The authors mention the term hyperbolic model. What does that mean?
0
votes
3answers
25 views

Does Mohs scale of mineral hardness always hold?

According to Wikipedia's article on the Mohs scale of mineral hardness, materials / minerals with a higher rating cannot be "visibly" scratched by materials with a lower rating. It goes on to admit ...
0
votes
1answer
59 views

Could anti matter collisions be or make dark matter?

I've recently seen that space is or could be a quantum vacuum full of particles like matter and anti matter appearing and possibly colliding causing in theory the same effects that dark energy has. My ...
0
votes
1answer
52 views

Two related questions about double-slit experiments moving at a relativistic speed

I was wondering as how would appear the interference pattern of a double-slit experiment moving at a relativistic speed v, 1) in the case of light and, 2) in the case wave matter (i.e. electrons for ...
-2
votes
0answers
40 views

What happened to the International Earth Rotation and Reference Systems (IERS) website? [on hold]

The IERS website has been down for several weeks now with no information about its return. The server returns a fatal error. Does anyone have news?

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