# All Questions

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### Does a crushed ice cube and a regular ice cube have different potential energies?

For a question on an heat transfer experiment on melting ice cubes in water and measuring the temperature decrease in water, there was a question that asked: Suggest the effect, if any, of crushing ...
0answers
6 views

### The transversality axiom in Lieb's Thermodynamics paper

I'm reading The Physics and Mathematics of the Second Law of Thermodynamics and have a question about the T4 transversality axiom which is writtern on page 54. T4) Transversality. if $\Gamma$ is ...
0answers
16 views

### Lifting the square root of a Lagrangian with potential creates cross-terms?

In a personal research project, I have derived the following Lagrangian density. $$\mathcal{L}=\sqrt{\eta^{\mu\nu} \partial_\mu \phi\partial _\nu \phi} + im\phi$$ When squared, my result looks ...
0answers
16 views

### Calculate the time taken for a body to hit earth's surface [on hold]

Find the time taken for an iron cube of dimensions 0.1m × 0.1m × 0.1m, whose density is 7.85 g/cm³ to reach the earth's surface released from a height of 10m from earth's surface, provided gravity = 9....
2answers
34 views

### What is the value of the inner product $_x\langle+|-\rangle$?

I know that $\left|_x\langle+|-\rangle\right|^2 = 1/2$, so is it just as simple as taking the square root of $1/2$? Thanks.
0answers
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1answer
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### How do we calculate work and heat for something that is not an ideal gas?

To make learning an easier process, things are considered simple and ideal. That is great, and in the case of thermodynamics it makes calculating heat and work transfer a simple thing that is easy to ...
0answers
12 views

### How to calculate energy loss by eddy current?

I was reading this post: Method of calculating eddy currents of a conductor, is this correct? and I found it very interesting. They came to the conclusion that the power lost due to eddy currents was: ...
3answers
81 views

### Reference frames versus coordinate systems

I have the following distinction clear in my mind: Reference frame → state of motion of the observer Coordinate system → set of numbers used to map the space points within a reference frame So for ...
0answers
22 views

### Parallel rays hitting a parabolic mirror at an angle [on hold]

I was thinking about parallel rays hitting a mirror that has a parabolic horisontal cross-section and a linear (straight) vertical cross-section. I can't understand what would happen if the rays came ...
1answer
28 views

0answers
29 views

### Can a huge mass on the L1 or L2 change the earth's orbit? [on hold]

question is clear L1: Lagrange 1 point L2: Lagrange 2 point
0answers
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0answers
33 views

### Rigid body dynamics exercise

Yesterday I came across this exercise and I can't really find a way to get the correct answer. Exercise A rigid homogeneous rod that weighs $M=5\,\mathrm{Kg}$, has length $l=0.8\,\mathrm{m}$ and a ...
0answers
46 views

### Can a radar detect non-solid bodies?

Would a radar detect a body of hot gas or plasma? A normal cloud? Would it detect dark matter? Could you tell the difference or would you believe radar sees a solid body? P.S. This is not a ...
0answers
27 views

I have been reading some papers which find all three components of the vorticity vector for a Fourier expanded (perturbation) velocity field i.e $\mathbf{u'}(x,y,z,t)=\int\mathbf{\hat{u}}(x,y,t)e^{... 1answer 33 views ### Main decay of$ J / \psi $The main decay of$ J / \psi $is$ c \bar{c} \to ggg $. How can this reaction channel be observed? 3 gluons will hadronize immediately, or not? 0answers 21 views ### Why interaction operator in 2nd quantization form is$V=\int dxdx' V(x-x') \rho(x)\rho(x')$? The question is as above, where$V\$ is a two-particle operator whose value depends only on relative coordinate. I am asking this question because I think the result should be not there. My claim: It ...

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