Cedric H.
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 Nov 12 comment Mathematica to help for an Hamiltonian problem Thanks, it is not exactly what I was looking for but it might do the trick. About the tags: these two can be made synonyms. Nov 11 comment Quantum Field Theory cross sections integrals +1: great link ! Nov 11 comment How do neutron stars burn? Is it decay or fusion or something else? It doesn't burn. Nov 10 comment Why doesn't a bike/bicycle fall if going with a high speed? @Adrian: you are saying "inertia" because... there is no force... In the case of the rope, the rope is providing a centripetal force. Nov 10 comment Why doesn't a bike/bicycle fall if going with a high speed? just to be a bit provocative: You are standing upright on your bike, you violently lean on one side, just at the beginning what is the direction of the centrifugal force ? Nov 10 comment Why doesn't a bike/bicycle fall if going with a high speed? Then you should thought of reading wikipedia in more details. And this: "you get centrifugal force (as oneat correctly pointed out)" is in no way true: imagine yourself in the inertial frame moving with the bike: no speed, so what ? @Davis answer is short but correct. Nov 10 comment Why doesn't a bike/bicycle fall if going with a high speed? This is a very misleading answer: there is no "centrifugal force", just a centrifugal pseudo-force in a rotating frame. When you look at a bike you generally do not consider a rotating frame, and even if you do, how would you relate the rotational speed of the frame, leading to a centrifugal term to the speed of the bike ? Nov 10 comment Why do we automatically assume that the velocity vector $\vec{v}$ and location vector $\vec{r}$ are independent? And think about real cases as in the first part of my answer. You can then easily deduce if v is independent of x or not. Nov 10 comment Why do we automatically assume that the velocity vector $\vec{v}$ and location vector $\vec{r}$ are independent? Just forget about all these things about the link between v and x. I think there is a big confusion about all this in your question. Start from the basics and try to understand the second part of my answer. Nov 10 comment Simple three-body-problem? Solution to a three-body problem exist when the three bodies are aligned as in your example. Nov 10 comment 4th equation of motion What are these four equation of motions ? Looks like it doesn't "exist"... Nov 10 comment Maxwell equations: how to know the behavior of charge and current? @Fiktor: This is called "conduction current" and applies in materials. For example it does not apply for "convection current" where real charge displacement is involved like in a particle accelerator or in a cathodic television. In the second case, your objection about magnetic field is valid and this is completely different story. Nov 10 comment Would a magnet attract a paperclip indefinitely? I am not saying that. And a plate cannot be "not moving" and sinking at the same time. Nov 9 comment How much force would be necessary to hold a 6-foot steel staff weighing 20 lbs from one end of it, parallel to the floor? Now I realize the point of the discussion on meta about SI units. I said it about CGS units, but this works for these also: should I cry ? :p Nov 9 comment In interferometry, what is the origin of the name “Airy function”? In the paper in French he uses the term "Airy formulas" like a well known name for these formulas... maybe defined in one of his earlier paper ? Nov 9 comment Would a magnet attract a paperclip indefinitely? @David: I edited to reflect what I meant. I think like that it is OK. Nov 9 comment Would a magnet attract a paperclip indefinitely? Latex is not working for this equation ? It looks OK for me. Nov 9 comment Why do we automatically assume that the velocity vector $\vec{v}$ and location vector $\vec{r}$ are independent? I don't understand you question. In any case the speed v is the time derivative of x. Nov 9 comment Mathematica to help for an Hamiltonian problem The area of the islands of stability around the elliptic fixed points. The integral of the separatrix (on both sides) if you want. Nov 9 comment Derivation of the centrifugal and coriolis force @Robert: What's the difference ?