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 Jan 9 comment Calculating Fraunhofer diffraction patterns The homework tag was not there, if I recall correctly, but even if it was, I was not aware of this policy. I will abide in the future... Jan 8 answered Calculating Fraunhofer diffraction patterns Jan 4 comment Which symmetry is associated with conservation of flux? Could you give a different example? The example you gave is not a conservation law, but merely an integral formulation of the fact that $\nabla^2 \phi=\rho$. Also, when introducing relativistic effects, it is not true anymore. Jan 3 awarded Analytical Jan 2 answered What is the rationale behind representing a state function by a complex valued function in QM? Jan 2 comment Conjugate Variables and Fourier Transforms in Classical Physics Why do you say that this is the case in QM? Very loosely speaking, the momentum is the Fourier transform of $q$, not of $V$. Jan 2 revised What does a unitary transformation mean in the context of an evolution equation? forgot a kronecker delta Dec 28 answered Determine the tensor of contraint and deformation of a cube under compression Dec 28 comment Numerical simulation of mechanics problem Euler's method is indeed unstable. If you want to write a solver yourself you will probably want to use 4th order RK integration, which is very well explain in wikipedia - en.wikipedia.org/wiki/Runge%E2%80%93Kutta_methods Dec 27 awarded Altruist Dec 24 answered absolute defintion of the right (i. e. not left) direction Dec 21 awarded Investor Dec 21 comment Free surface of inviscid fluid flow (1) I agree with the fellows above me on this point - inviscidity does not imply $\partial_y v_x=0$. (2) if at $x_1$ the velocity is independent of $y$, then because it is horizontal at $y=0$, it must also be horizontal for $y=h(x_1)$, and therefore it $\partial_x h(x_1)=0$, and the tangent to the free surface will be horizontal on the left side. (3) The problem is not defined if you don't specify the full profile of $\vec v(y)$ at both edges of the problem. (4) This is a very nice question! I'm setting a bounty. Dec 20 answered What does a unitary transformation mean in the context of an evolution equation? Dec 18 comment How much does a steel spring wire bend due to it's own weight? You used diameter or 1.3 mm in your formula. Here you give 1.2mm or 1.5mm. Dec 18 awarded Critic Dec 17 comment Who is right? Force exerted on a body. Me or my friend? The problem isn't clear to me. Are the springs hanged from the ceiling or is each mass attached to the one above it? How come the elevator is motionless and accelerating? Dec 17 answered Does opening the oven door heat the house more than if the door is closed? Dec 17 comment How much does a steel spring wire bend due to it's own weight? Oh, and another thing - I took $L$ to be the length from the point of support to the end, but re-reading you question makes me think that $L$ is total length. If that is the case, you should divide all my answers by $2^4$ to get 5.9cm and 3.8cm. Dec 17 comment How much does a steel spring wire bend due to it's own weight? Maybe. Note also that using a wire of double diameter will decrease the deflection by a factor of 4, so that might also bbe a solution.