Ben Crowell
Reputation
30,910
105/100 score
 Oct 23 comment If friction disregard area, why the direction you drag a long object matters? Oct 23 comment If friction disregard area, why the direction you drag a long object matters? I tried the experiment with the ruler, and I couldn't feel any clear difference. Oct 23 revised Center-of-mass frame for massless particles added 351 characters in body Oct 23 comment What conditions should be met to notice a Doppler effect on light? I don't get it. Where does the 3 come from? Oct 23 awarded Nice Answer 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 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.