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Oct
23
answered Center-of-mass frame for massless particles
Oct
23
comment How can Lorentz contraction be “directly” measured?
There are plenty of high-precision experiments that show relativistic effects without the necessity of accelerating anything to a significant fraction of $c$. A good example is the famous Hafele-Keating experiment.
Oct
23
answered How can Lorentz contraction be “directly” measured?
Oct
23
revised Sound diffraction through a single slit
added 548 characters in body
Oct
23
comment Black hole “no hair” theorem
Electric charge isn't quite as special as you're thinking. The no-hair theorems you usually hear about are for electrovac assumptions. So the special role of electric fields as opposed to any other fields is put in as an assumption. There are known counterexamples if you allow other fields. See livingreviews.org/lrr-1998-6 .
Oct
22
comment Why GPS is at LEO?
@JerrySchirmer: That's not quite right. The usual goal is to locate yourself on a map, i.e., horizontally, and for that you get the best accuracy when the satellites are close to the horizon.
Oct
22
comment Sound diffraction through a single slit
I wasn't the person who flagged it as low quality, but the original answer was only one sentence.
Oct
22
comment Sound diffraction through a single slit
I don't think this is right, for the reasons given in my answer. Note that I gave three separate mechanisms for the diffraction to behave differently.
Oct
22
comment Sound diffraction through a single slit
@Floris: You could also worry about the dielectric constant of the material, etc. You can't just assume a material with no electromagnetic properties -- such a material would be perfectly transparent.
Oct
22
awarded  Cleanup
Oct
22
revised Sound diffraction through a single slit
rolled back to a previous revision
Oct
22
revised Sound diffraction through a single slit
added 247 characters in body
Oct
22
answered Sound diffraction through a single slit
Oct
22
comment Sound diffraction through a single slit
related: physics.stackexchange.com/questions/5886/… physics.stackexchange.com/questions/141562/…
Oct
22
comment Recommended books for undergraduate electrodynamics
@ChrisWhite: No way. Jackson has much more depth and breadth than Purcell. I learned E&M from Purcell as an undergrad and had Jackson in grad school, and there was a ton I learned from Jackson.
Oct
22
answered For a massless pulley moving upwards with acceleration, is the upward force equal to the downward force?
Oct
22
comment For a massless pulley moving upwards with acceleration, is the upward force equal to the downward force?
The force equations you provided are wrong. He's applying Newton's second law to the pulley, which is perfectly legitimate.
Oct
22
comment For a massless pulley moving upwards with acceleration, is the upward force equal to the downward force?
I see. I edited the question a little and retracted my close vote.
Oct
22
revised For a massless pulley moving upwards with acceleration, is the upward force equal to the downward force?
clarify based on comments
Oct
22
comment For a massless pulley moving upwards with acceleration, is the upward force equal to the downward force?
Clearly, since there is a net upward force, the pulley itself will accelerate upwards. Huh? Why doesn't the whole apparatus just drop?