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 Dec 15 awarded Yearling Nov 3 awarded Revival Jul 10 answered Effect of boundary conditions on partition functions Jun 26 awarded Nice Answer May 24 comment Crushing a magnetic field I would suggest to add a "mumbo-jumbo" tag. May 1 comment A conceptual problem with Euler-Bernoulli beam theory and Euler buckling @Raskolnikov No, it has 2 derivatives less. May 1 awarded Student May 1 asked A conceptual problem with Euler-Bernoulli beam theory and Euler buckling Apr 2 comment Power laws and deterministic systems This is a totally different question. The answer, in short, is that a deterministic system can be described deterministically. Very often, however, you can't do that because the system has too many degrees of freedom (e.g. sand-piles) so that a full deterministic solution is both infeasible and useless. In such cases, a probabilistic description usually casts more light on what is going on. Apr 1 comment Deriving the Lagrangian for a free particle I think the best advice one can give you is don't read Landau & Lifshitz. They are great books for reference, but practically impossible to learn from. If you're into analytical mechanics then Goldstein is a good place to start, or Arnold, if you're more interested in the mathematical aspects. Mar 29 comment Is there analysis library for stress-strain data? In that case, send my your credit card number and I'll do it for 500$! Mar 29 comment Is there analysis library for stress-strain data? I don't know of any software, but at least for the Young's modulus, yield stress and work it will be very easy. I doubt that you can get the fracture toughness from these data. Mar 21 comment Calculating Ground State Energy in 1D Potential This is exactly the point. As the particle is large, it is localized. The localization will be around the minimum of the potential. Could you write up a solution and post it, answering your own question? Mar 19 comment How many photons does it take to measure a linear polarization? What do you know about the measuring device? If it is perfect then you can get an exact result (as many bits as you like) with two measurements. Mar 19 awarded Citizen Patrol Mar 15 awarded Necromancer Mar 8 comment Find drag force on link of rotating chain If the link is infinitely small, then the force will also be infinitely small. I think what you're looking for is force density Mar 5 comment Why are scattering matrices unitary? Mar 5 comment Why do steam bubbles increase in size as they rise? Why did you turn down the simpler explanation - that as the bubbles rise the surrounding pressure decreases, and they simply expand ($V=\frac{Nk_bT}{P}$) without transfer of mass or energy? Feb 20 comment Force from point charge on perfect dipole The general formula for the force is, as you correctly stated$F=q\Delta E$, which is conveniently written in a geometrical form as the dot product $$\vec F=\vec\nabla\vec E \cdot q\Delta\vec r =\vec \nabla\vec E \cdot\vec P$$ Note that$\vec\nabla\vec E$is a matrix. However, when you work in any other coordinate system, the gradient$\vec \nabla\$ is no longer the simple expressions that you are used to. You can derive the formula for it by differentiating the expression $$\vec E=E_r\hat r+E_\phi \hat \phi+E_\theta\hat\theta$$ and remembering that the unit vectors are also space-dependent.