# All Questions

3answers
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### Dissipate laser light in a surface

Im building a laser target. It consists of a box, with a black plexiglass circle in the center of one of its sides, and a larger white circle around it. The black for the inside shots, and the white ...
0answers
6 views

### Do metric theories with torsion contradict solar system observations?

Obviously, the answer to this question can be "maybe, if you make the torsion tensor small enough", but my question is, given some "typical" size to the torsion tensor, do the spin-orbit couplings ...
1answer
15 views

### Circle of light by a laser and wire

I've asked a question before about this phenomenon, see it here Diffraction in Circle of light? or here Laser, wire, and a circle of light But there are some fringes in that circle of light and I ...
0answers
4 views

### Derivation of the Stuart Landau time dependent amplitude time evolution equation for Hopf or Pitchfork bifurcations

I am studying the Hopf / Pitchfork bifurcations, the ordinary differential equation of which is: $$\dot x = x \ (\rho - x^2)$$ Which is a cubic order equation which describes the time evolution of ...
0answers
13 views

### Intersection of two moving objects

There are two objects. The first object moves with speed U1 from known point A to known point B. The second object has speed U2 and starts from known point C. What is the direction the second object ...
2answers
21 views

### How are determined experimentally the energy levels of the atoms ? How is the calibration done to several decimal points?

I see discrepancy for the absorption edges for the atoms in the X-ray ? For example K-absorption edge of carbon can be anywhere between 282 to 284eV according to different sources. My question is ...
2answers
7 views

### Is air infiltration a type of convective heat transfer (convection)

I have a building / physics question... A major source of heat loss in homes and buildings is infiltration through cracks (warm air from inside seeping out). Wondering if this falls in the category ...
0answers
17 views

### newtonian-mechanics

A 1000Kg helicopter hovers over a forest fire and starts to squirt water downward with a speed of 10m/s at the rate of 40Kg/s. What is the initial upward acceleration on the helicopter when it first ...
1answer
33 views

### Is UV catastrophe same as IR catastrophe?

I am currently studying quantum physics from Serwey-jewet. Where in the topic of Planck's law, infrared catastrophe is alternatively used for UV catastrophe while explaining how Plancks constant ...
0answers
19 views

### Does the entropy of the universe change as expansion exceeds the speed of light?

The potential encoded information in a photon that is at the edge of the observable universe would seem to be lost as the universe expands. Does that loss of information contribute to the overall ...
0answers
37 views

### The Golden Ratio and universe

It is well known that golden ratio is "almost everywhere", also it is in Milky Way galaxy Can general relativity (or Newton's gravity) explain why the arm of Milky Way galaxy is approximately ...
2answers
28 views

### How do we know the boundaries of a wavelength?

So the length of a wave is the distance between two compressed regions as shown in this representation of a longitudinal wave: But how do you know exactly where the two points are? Is there a point ...
0answers
41 views

### Closed timelike curves in the spin-2 gravity formalism

Let's say we take some topologically trivial CTC spacetime, like the Gödel metric : $ds^2 = -dt^2 - 2e^{\sqrt{2}\Omega y} dt dx - \frac{1}{2}e^{\sqrt{2}\Omega y} dx^2 + dy^2 + dz^2$ And then I ...
0answers
37 views

### Why does specific heat increase with temperature?

Except for monoatomic molecules, specific heat increases with increase in temperature. Why?
0answers
43 views

### Question on time dilation

When i studied physics we had this example where someone climbes into a rocked flyes into space comes back the time that passes for him one year time on earth 86 years. I think most know what thinking ...
0answers
10 views

### Is Isochoric compression or expansion possible?

Stirling cycle is made of two isothermal and two isochoric processes. Heat is added isothermally, expansion and compression takes place isochorically, as given by the book. How can a gas be ...
4answers
205 views

### Does a person inside a falling bus fall to the front of it?

So I was watching Final Destination 5 and something caught my attention. There's a part where a bridge collapses and everything falls apart, so there's this bus that has a person inside (unaware of ...
1answer
17 views

### Work done by friction on a body?

I know that when a body slides over a surface, the work done by friction is not stored as potential energy in the body. It is dissipated in the form of heat. But why is it not stored as potential ...
0answers
22 views

### Would momentum be conserved in teleportation? [on hold]

Defining teleporation loosely as at least quantum tunneling all of your particles and preserving the arrangement. If that doesn't work, assume the mechanisms of the most basic definition of ...
1answer
66 views

### Why does hitting a cold bag of water freeze?

About 24 hours ago, I bought a box of 30 pieces water ice. I put them in the freezing compartment and when I came from work I was expecting a nice chilling ice. But when I opened the freezer, I saw ...
1answer
9 views

### The working of rheostat/ potentiometer

I can't grasp the concept of how a rheostat divides potential and acts as a variable resistance in a circuit.I have tried asking my teachers and fellows but their explanation hasn't been satisfactory. ...
0answers
16 views

### Resonance Stabilization of a mass-spring system

Given point-masses connected by loss-less springs and a specific initial kinetic energy distribution. What mathematical tools exist to analyze the system for resonance stabilization. This problem ...
1answer
29 views

### Can the entropy of a part of a closed system become less than the initial entropy of the entire system?

I am reading Sir Roger Penrose's book "What came before the Big Bang?". Here, I came across a chapter where he talks about how sunlight provides us energy in low entropy and how through various ...
1answer
20 views

### Book suggestion for introductory plasma physics

I have an undergraduate background of electrodynamics, special theory of relativity and quantum mechanics. I would like to study plasma physics by myself so please suggest a few introductory books on ...
0answers
15 views

### Moment of inertia of a connecting rod in a crank-slider mechanism

PROBLEM I am trying to determine the moment of inertia of a connecting rod (conrod) in a crank-slider mechanism. $r$ is the crank radius. $l$ is the length of the conrod. $I_{rod}$ is the moment of ...
1answer
22 views

### from microscopic to kinetic transport theory

One way to model the dynamics of particles is to find the differential equation of motion of a particle. Of course, this will be nice and easy to do if we have only a few particles (like one-ish, ...
1answer
31 views

1answer
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### Question about force in transverse waves on a string

In deriving wave equation or power transmission of wave transmitted by a string, it is usually stated (with some assumptions) that the transverse force on a point of the string is proportional to the ...
1answer
24 views

### Force acting on a dipole placed in a non-uniform electric field

Why does the net force acts in the direction of increasing electric field when an electric dipole is placed in a non-uniform electric field?
1answer
35 views

### Raychauduri equation for Milne universe

I am trying to solve this kind of problem: Consider the Milne model, i.e., the empty $\kappa = −1$ Friedmann model. Verify by a direct calculation that the expansion $\Theta$ of the unit ...
0answers
35 views

### QED renormalization: mass and dirac field

Why the mass renormalization $Z_m$ and the field renormalization $Z_\psi$ in QED (MS-renormalized) does not contribute to the beta function computation? From Ward identity, I know that $Z_A=Z_e^{-1}$, ...
9answers
2k views

### How to emulate 40ft of water

I am part of an underwater robotics team, and our next year's challenge requires us to compete at a depth of 40ft. We don't have any pools nearby to test in, so I want to emulate this 40ft of pressure ...

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