# All Questions

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### Tunnelling from a normal metal into a superconductor

a similar question has already been asked in the forum but unfortunately I cannot yet comment and still think that some things left unanswered. My question is in general concerning the tunnelling ...
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### Equation of string as hamiltonian field equations

I am using Hamiltonian field theory for the first time and I struggle with some final steps. The task is to derive the equation of vibrating string using Hamilton's field equations. Here is what I ...
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### What mechanism explains the effect of a hot surface on hydrogel balls?

Adding little hydrogel balls to a hot surface has an interesting effect as seen in this video. Hydrogels (as the name suggests) contain a lot of water but rather than melt or burst, the little balls ...
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### Special Relativity in water

If there are 2 observers in water moving relative to each other as well as to water, they measure different speeds of light. So does time dilation occur for them? (since Time dilation is based on ...
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### Bernoulli Principle and pressure function

I have read in several places now that for compressible flow the Bernoulli equation $$\frac {v^2}{2}+ P\ + \Psi = \text{constant}$$ requires: $$P=\int {dp\over \rho(p)}$$ But I don't get ...
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### Object Falling on spring

This is problem #23 from the 2015 F=ma contest: A 2.0 kg object falls from rest a distance of 5.0 meters onto a 6.0 kg object that is supported by a vertical massless spring with spring constant k ...
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### Crest in Light Doppler Effect

The way it is explained in wiki Doppler effect in sound happens because waves of particles with biggest density called crest hits our eardrums more often if object is moving towards us (increased ...
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I need to study non-uniform magnetisation and the only book where I found this was Berkeley Physics Course Vol.2. Is there other book's options to this issue?
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### A rope between Earth and Moon - Length and Speed of Light [duplicate]

An earlier question was asked on what would happen if a rope was attached between Moon and Earth, but the question was more about the impacts in terms of geology. We keep the same experiment setup : ...
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### Finding diffeomorphism given vector fields [closed]

Given a vector field how do you find the associated diffeomorphisms? Say I am given a vector field in Minkowski space $$\xi = x \frac{\partial}{\partial t} + t \frac{\partial}{\partial x}.$$ How do ...
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### Sticky physics of pasta mixture [duplicate]

When you mix cooked noodles or other "prevailing 1D pasta" like spaghetti with other ingredients like olives, pieces of meat (not minced) etc. you will probably experience the fact, that the mixture ...
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### Conservation of Angular Momentum…or not?

This is my first post on physics stack exchange, but I thought the question was more appropriate than on that of math.stack. I'm currently designing a crude model of the sun-earth orbit (which I have ...
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### A fast object (0.8c) getting overtaken by another fast object (0.9c): why don't times agree?

I'm trying to work on an exercise in Wolfgang Rindler's book "Introduction to Special Relativity" and I'm stuck on the following exercise: Two particles move along the x-axis of S at velocities 0....
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### When can we just look at just the partial derivative of energy?

I am reading a text about fluid mechanics and in the chapter about the (zero viscosity) Wuler equation this showed up: We consider now the kinetic energy and the internal energy of the system and ...
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### Has this double slit experiment been performed with electrons?

I don't know if we have the technology yet. Double slits, one electron at a time. The moving electron should produce a magnetic field. Can we detect such a weak magnetic field and tell which slit ...
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### Pseudoscalar current of Majorana fields

Consider a Majorana spinor $$\Phi=\left(\begin{array}{c}\phi\\\phi^\dagger\end{array}\right)$$ and an pseudoscalar current $\bar\Phi\gamma^5\Phi$. This term is invariant under hermitian conjugation:...