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Feb
27
comment Whistle Physics
Yes it is a kind of vortex shedding. Perhaps this is what you are looking for? www2.ibp.fraunhofer.de/akustik/ma/pipesound/animEdgeTone.mpeg
Feb
27
revised Practical method to weigh human limbs with common household items?
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Feb
27
answered Practical method to weigh human limbs with common household items?
Feb
27
comment Where's the energy in a boosted capacitor?
I'm not sure where my argument is flawed. The same conclusion can be reached by calculating the momentum of the rod and using the fact that the rest mass of the rod is zero to calculate the energy of the rod in the boosted frame.
Feb
26
comment Where's the energy in a boosted capacitor?
There won't be any physical change happening on the capacitor during this changing process. The only thing is that the energy/mass that was hidden in rod 1 is simply transferred to rod 2. The purpose of changing rod is just to determine the amount of energy hidden inside the rod. The rod is part of the system and we need to include it in the energy calculation.
Feb
26
comment Where's the energy in a boosted capacitor?
I think it is not quite a problem, we can always recreate the starting condition. Suppose that initially there is already a rod between the plates, call this rod 1. Then at $t=0$, this rod suddenly disappears and rod 2 suddenly appears to replace it. From the point of view of the rest frame of capacitor, doing this won't change the energy of the system. And thus it must be so in any other frame. In the moving frame, rod 2 does not receive work from the left plate and the right plate simultaneously. Thus some energy is transferred into rod 2. And this energy must be taken into account.
Feb
26
comment Where's the energy in a boosted capacitor?
I was't saying that the capacitor is accelerated. I mean the plates are attracting each other through electrostatic forces, so if there is nothing that counters these forces(i.e. a rigid rod) the plates will crash into each other. Now if there is a rod between the plates everything looks the same as in the problem description, I know that we are just viewing it in a moving frame. But the rod plays a role here. In the frame where the capacitor appears to be moving, the rod does work on the capacitor. And the total work turned out to negative, as a result the rod's mass is increased.
Feb
25
answered Where's the energy in a boosted capacitor?
Feb
24
answered Whistle Physics
Feb
24
awarded  Popular Question
Feb
23
awarded  Informed
Feb
22
revised What happens to the magnetic field in this case?
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Feb
22
comment What happens to the magnetic field in this case?
Yes all the field lines coming out from the north poles will end up in the south poles by squeezing through the small opening. However the magnetic flux itself is weakened as a whole when we put the pieces together. The outer field exists in order to preserve $\int \vec{B}.\vec{dl}=0$. By putting the pieces together we decrease the $ \int \vec{B}.\vec{dl}$ inside the "meat" of the magnet, therefore the field outside the magnet is reduced. So even though the field lines get squeezed more, the number of field lines coming out of the north poles is also decreased.
Feb
21
answered I don't understand the relationship between electron indistinguishability and the Pauli exclusion principle
Feb
21
comment What happens to the magnetic field in this case?
Also we don't need so much energy to insert the last piece of magnet, the field is already quite weak before the insertion. Can the downvoter please explain?
Feb
21
comment What happens to the magnetic field in this case?
I don't see why it will create a non-physical magnetic configuration. Can you specify what rule might be violated ? I think it's okay for the magnetic field outside to disappear entirely, it doesn't mean that the interaction energy will also go away with it. Higher potential energy(depends on negative of the cross term of magnetic energy density) doesn't always mean higher total field energy, because only part of the field energy is responsible for interactions(force). The final configuration will have a very high potential energy and tends to blow up, but there's no singularity involved here.
Feb
21
revised What happens to the magnetic field in this case?
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Feb
21
revised What happens to the magnetic field in this case?
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Feb
21
revised What happens to the magnetic field in this case?
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Feb
21
revised What happens to the magnetic field in this case?
added 30 characters in body