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 Oct 26 comment Why is general relativity only formulated in continuum terms? Poisson's equation related to continuous mass distribution. The version that related to discrete mass distribution is simply one that defines the potential field as the sum of potential fields $-mG/r$ generated by each discrete point particle. What is the GR equivalent? Oct 25 comment Why is general relativity only formulated in continuum terms? I don't understand. In Newtonian Mechanics, space (and time) is continuous, but yet particles are discrete beings and we can formulate the theory as it applies to them. Oct 12 comment Equivalences and derivations in Newtonian/Classical Mechanics Perhaps you can expand on that in your answer (with a short proof or a source)? Thanks! Oct 12 comment Equivalences and derivations in Newtonian/Classical Mechanics So, what about the other way around? How does one show if the Second and Third laws a consequence of the conservation laws? Oct 12 comment Equivalences and derivations in Newtonian/Classical Mechanics I saw this in: proofwiki.org/wiki/Conservation_of_Angular_Momentum Oct 12 comment Equivalences and derivations in Newtonian/Classical Mechanics Thanks. I thought conservation of momentum is a derivation of the second law (which just state the sum of all momenta doesn't change), and that conservation of angular momentum is a consequence of the third law (e.g. the proof in wikiproof). May 28 comment Symmetry of the $3\times 3$ Cauchy Stress Tensor I'll try. Also see the clarification to my question, if you haven't already. May 28 comment Symmetry of the $3\times 3$ Cauchy Stress Tensor Thanks - the Gurtin explanation sounds promising. Can you write some more details, or alternatively link to the relevant parts of the book? May 28 comment Symmetry of the $3\times 3$ Cauchy Stress Tensor Thanks for the comment. I'm not sure this answers my question - I edited it for clarification. May 19 comment Symmetry of the $3\times 3$ Cauchy Stress Tensor While I can convert them when I have a metric, I still think there is a distinction in the way to think about them. This is particularly true when generalizing to SR or GR, where they don't have the same coordinates. May 4 comment Why is the (nonrelativistic) stress tensor linear and symmetric? The stress tensor is a function a given $n$ to $T(n)$. The equality you are describing refers to integration over a surface $S$ with varying $n$s. How from that equation over general $n$s I get some reasoning about a given $n$? Thanks! May 3 comment Why is the (nonrelativistic) stress tensor linear and symmetric? I like the method in this answer, but still missing some details. In the first part, is there implicit summation over $j$? More importantly, a volume element with surface $S$ has a changing $n$; how does the stress tensor enter this calculation? Jan 9 comment Good book for Analytical Mechanics This book explicitly deals with differential geometry, which I would like to avoid. Apr 3 comment Photon hitting an atom with higher energy than needed to ionize So will the photon be absorbed completely and the electron will have the excessive energy (as kinetic energy)?