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 Dec 22 awarded Yearling Oct 2 comment Why is boron so good at neutron absorption? @user43087: The point John is making is that the neutron should not be considered an infinitesimal point; it is effectively delocalised (spread out) over a larger radius. The interaction is governed by the set of available energy states for the combined system, and here the nuclear forces can come into play. The 'cross section' is not a measure of how far away the neutron can be, but of the probability of the interaction taking place. As John points out, the size of different nuclei is largely unimportant. Sep 15 comment Is This Educational Model of Electron Any Good? The particle vs wave behaviour is not the electron changing from one to another. They are just analogies we can grasp which describe aspects of the electron's behaviour. When a large system interacts with an electron (e.g. you measure its position) no energy is necessarily given to or taken from the electron, but the interaction does affect the state of the electron. In deterministic interactions the electron has to yield a valid deterministic answer so the wavefunction is said to collapse - really this is not well understood but it is more like a selection. It is not a particle or a wave. Sep 15 answered Is This Educational Model of Electron Any Good? Jul 1 comment How to emulate 40ft (12 m) of water? +1 for pressurised air above the water. Jun 29 comment Why can't the Navier Stokes equations be derived from first principle physics? Disagree on the first paragraph - we use useful equations covering bulk behaviour which could be derived from simpler principles because it is easier to use (where the derived relations are sufficient). $PV = nRT$ is not fundamental, and it breaks down for anything too far from an ideal gas. But no-one would throw it away when considering gas behaviour for a combustion engine, for example, because starting from first principles would get you to the same, or worse result given an amount of resource effort. Jun 24 answered Generalization of torque and angular momentum Feb 3 comment Why do most formulas in physics have integer and rational exponents? Actually, as orion points out, there are important mathematical reasons for linear equations, so the value of the exponent is not arbitrary Dec 8 comment Electromagnetic waves should stop while encountering a conducting shell? I've added a little information on surface plasmon resonance, but if you have more questions, please do post a new question to attract good answers! Dec 8 revised Electromagnetic waves should stop while encountering a conducting shell? added 660 characters in body Nov 28 comment A question about motion and time dilation @user43783: Congratulations, this is what General Relativity is all about. Begin by remembering that there is no absolute position, and no absolute time. Nov 28 answered How does air in a water balloon act in space? Nov 25 comment Why does iron sink in molten iron instead of floating? I think your densities are wrong. At present you have a higher density of ice at 0 C, which would make it sink. Nov 25 answered Electromagnetic waves should stop while encountering a conducting shell? Oct 1 answered Correct approach for calculating excited states of circular quantum dot under effective mass approximation Sep 30 awarded Explainer Sep 30 revised Correct approach for calculating excited states of circular quantum dot under effective mass approximation Added paper name, authors etc, made a more specific title Sep 30 comment Correct approach for calculating excited states of circular quantum dot under effective mass approximation I've added the equation, explanation, paper details and fixed the title so that people can see what it's about. Sep 30 suggested approved edit on Correct approach for calculating excited states of circular quantum dot under effective mass approximation Sep 15 comment How does an electron move around in an orbital? Is it “wave-like” or random? FYI, calculating the surface within which there is 90% probability is actually quite challenging unless the orbital is really simple and analytic. So usually what is plotted is just an isosurface on which the probability density is at a given figure, because that's much easier.