# All Questions

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### The magnetic field between two intersecting cylinders

"Consider a cable of infinite length whose section has the form of two intersecting circles of same radius $a$. The first part is then a cylinder of constant volume current density $J$ along the ...
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### Are there other less famous yet accepted formalisms of Classical Mechanics?

I was lately studying about the Lagrange and Hamiltonian Mechanics. This gave me a perspective of looking at classical mechanics different from that of Newton's. I would like to know if there are ...
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### Did God have enough water to flood the earth during Noah's time? [migrated]

In Genesis 7:11-20, we read how God destroyed the living beings on earth--save for Noah's family-- using flood. In the six hundredth year of Noah’s life, on the seventeenth day of the second ...
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### Why do $S_x$ and $S_y$ flip up/down spin states but $S_z$ does not?

By using the notation $S\lvert s,m_s\rangle$, such that $\bigl\lvert\frac{1}{2},\frac{1}{2}\bigr\rangle=\lvert+\rangle$ and $\bigl\lvert\frac{1}{2},-\frac{1}{2}\bigr\rangle=\lvert-\rangle$ we can ...
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### Is a black hole a 3D hole? And doesn't it pull into the 4th dimension?

Hear me out here please: A body on a line (a 1-D world) causes a warp in the line, i.e. a curve (2-D) A body on a plane (a 2-D world) "sinks", causing a warp in the plane, i.e. a pit (3-D) Then does ...
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### Can information travel inside to outside the event horizon?

Lets suppose I am an immortal man and I have a very strong and long stick. We know that information cannot travel inside to outside the event horizon and as far as I know there is nothing special ...
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### Why don't we have logarithms or exponentials of the fields in the Lagrangians?

All tbe Lagrangian densities I have seen have always been polynomials of the fields. Is this a coincidence or is there a reason forbid, say, Lagrangians with logarithms or exponentials of the fields?
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### Regge trajectories for higher spins

I have read that Regge theory did/does predict higher spin meson states, but that at higher spins the data becomes fuzzy for spins greater than 4. Why is this so? In the book "A Brief History of ...
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### Why isn't the magnitude of the electric field in a circuit zero?

I've been re-reading my knowledge of circuits and how current flows as well as the surface charge distributions in the steady state, since it's been quite some time and we've just started studying ...
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### Why aren't we affected by radium?

1)We have radium clocks, watches, wrist bands and many things which glow because of radium but we know that radium is radioactive so why isn't it harmfull for us when in bands, watches etc. 2)Does it ...
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### What is the reason that EXAFS are done with monochromatic x-ray light?

Why is the light incident on the samples in EXAFS experiments monochromatic? What would happen if a broad bandwidth hits a grating and then all the diffraction spectrum goes through the sample and is ...
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### Mean value of number of molecules of a gas inside a volume

I'm trying to solve this problem in Statistical Mechanics but I'm not sure if my reasoning is right. The problem is as follows: we have a certain region with volume $V_0$ containing $N_0$ molecules of ...
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### Antineutron repelled by gravity?

I was reading an old post, Can gravity be shielded, like electromagnetism?. One of the responses had this comment. There are some experiments trying to measure whether antiprotons ( antimatter) ...
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### Why is earths gravitational pull only at its center?

Does acceleration due to gravity remain constant wherever I go in and on the earth?
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### Does the universe have a different age to different observers?

Although I understand that the universe is approximately 12 billion light years wide, and that may mean that it took the light photons 12 billion years at 186,000 miles per second to reach the ...
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### What is the pressure of falling water?

Imagine a breaking wave 10m high. The wave breaks onto a beach. What is the maximum pressure created by the wave on the beach, ignoring effects such as might be cause by air?
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### How to cancel $\mathcal{N}_3$ in the hierarchy equations for the neutrino moments? (Dodelson, eq (6.107))

I was trying to understand the Boltzmann equation (B.eq) for massless and non-interacting neutrinos, principally to solve one datail in the exercise $6.2$ of Dodelson. Given the Beq for neutrinos in ...
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### When moving from one position to another at a constant velocity, how does the conservation of energy hold?

I know that this might be a duplicate question, but I have not found any satisfactory answers that clear up my lack of understanding. Here is my question. Say a sloth hangs on a tree in the middle of ...
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### Frictional force [on hold]

a box of banana weighing 40N rests on a horizontal surface. the coefficient of static friction between the box and the surface is 0.4 and coefficient of kinetic friction is 0.2. a. if no horizontal ...
### assuming $kT=1$ in $Z=\sum e^{-H}$ and $F=-lnZ$?
Some statistical physics book use: $Z=\sum e^{-H}$ and $F=-lnZ$ as defination for partition function and free energy. I think they should be $Z=\sum e^{-\frac{H}{kT}}$ and $F=-kT lnZ$ Are they ...