dmckee
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 Feb 14 comment Movement in outer space via Newton's law of every action has an equal and opposite reaction The assumption $\sum \vec{a}_i = \vec{a}_b$ is not obvious, and is suspect. You seem to be claiming that a person can impart a much lower acceleration to a single grain of rice than they can give to a whole bag of rice. On the other had you also have a mistake in your summation algebra: $\sum_i x_i y_i \ne (\sum x_i)(\sum y_i)$, so your first mistake does not drive your conclusion as far off as it would if you had done the rest of the math right. Feb 14 comment Why gravity decreases as we go down into the earth? Yeah, I got it when I looked at the plot. Fair enough. Feb 14 comment Are there any Meson colliders? Muon colliders are planned, but they have little to do with meson colliders. Feb 14 revised Why gravity decreases as we go down into the earth? latexify Feb 14 answered Sign of Work and potential energy in electrostatics Feb 13 comment Double slit experiment and representation of light waves In the representation here the curves mark the peaks of sinusoidal waves (and "gravity waves" on the surface of a fluid are sinusoidal in the limit of amplitude small compared to depth). This is just a different visualization. It is always important to distinguish between the visualization and the thing visualized. Feb 13 comment Relativity of simultaneity and cause-effect Probably useful to note that this work is done in $c =1$ units. Using SI units every occurrence of $t$ in the above should be read as $ct$ and every occurrence of $v$ as $v/c$. Feb 13 comment $\tau$ pair production question @Jeff The virtual photon is off-shell. It does not have to obey energy conservation the pair of tau-leptons is on-shell. It does have to obey energy conservation, but they are in the same potential well that the electrons were in (they have charges $\pm e$, too). If they were to move to separate to a great distance they have to give that energy up again, but if they bind they get to keep a some of it, an because the taus are much heavier than electrons ending bound is a possibility. Nor does the initial annihilation have to take place at rest; both SLAC and LEP did it at quite high energies. Feb 13 comment Relativity of simultaneity and cause-effect The important thing to keep in mind is that time ordering can only be reversed for space-like separated events. From that you can draw the correct conclusion about the possibility of causality reversal in special relativity. Feb 13 comment How does cold fusion work? RonM has a theory. I don't have the background to fully evaluate it, so I can't say for sure if it is worth considering. My big question about it is: does it give a hint why it is hard to reliably build cells that work and stay working? (Or has someone solved that already?) Feb 13 comment Maximum theoretical efficiency of internal combustion engine I don't think you are routinely getting down anywhere near 275 K for the low temperature limit...the gas comes out of the cylinders still hot. Don't touch the exhaust manifold if the engine is running or has been recently. Feb 13 comment Why Transmission of electrical energy without wires was not practical even after Tesla's proposal Because Tesla never really made it work. Microwave power transmission is a working technology, but it is not enormously efficient. Feb 13 comment $\tau$ pair production question " I believe they first need to overcome this potential barrier." @JeffDror The potential is negative (unlike charges attract, after all). But you only get energy back from that if the taus end bound. Feb 12 comment $\tau$ pair production question Another possibility. If the Tau-pair is produced almost at rest they could (in principle, I don't know if it is possible in practice) form a short-lived bound state at total energy just slightly less that $2m_\tau$. Feb 12 comment $\tau$ pair production question It may (or may not) be significant that particle physicists often use "energy" in this kind of context to mean the kinetic energy of the beam. Of course in the reaction in question the electrons will be in the ultra-relativistic regime so the difference is trivial, so that may not be what is intended. Feb 12 comment Would a considerably big asteroid be disintegrated by the Earth's Roche limit? @AbanobEbrahim Compute it using, say, $10^{-4}$--$10^{-3}\,\mathrm{m/s^2}$ to get a feeling for the time scale. Define "significant change" however you want, but I'd use a number on order of 1/10 the diameter at a minimum. Feb 12 comment Would a considerably big asteroid be disintegrated by the Earth's Roche limit? Yes. I was agreeing with you and amplifying your assertion with some (handwavy) math. Feb 12 comment What changes occur while an atom approches the speed of light? To emphasize John's first point: What the difference between “orbital” and “orbit”?. Feb 12 comment Why change in Capacitance? Go back to the beginning. How is the capacitance of a system defined. (Note, I don't mean the capacitance of a parallel plate capacitor, but of any system.) Now think about how your multiple-capacitor system behaves (in terms of charge and voltage) as compared to a single capacitor. Figure it out for yourself and you will know. Feb 12 comment True or false: the Moon was touching the Earth 1.2 billion years ago Various related posts: physics.stackexchange.com/q/31429 physics.stackexchange.com/q/47829 and I think there are a couple of others. Also one of the answer to that first link is pretty close to what you want to know.