Friday 26 January 2018

homework and exercises - Explanation: Simple Harmonic Motion



I am a Math Grad student with a little bit of interest in physics. Recently I looked into the Wikipedia page for Simple Harmonic Motion.


Guess, I am too bad at physics to understand it. Considering me as a layman how would one explain:



  • What a Simple Harmonic motion is? And why does this motion have such an equation $$x(t)= A \cos(\omega{t} + \varphi)$$


associated with it? Can anyone give examples of where S.H.M. is tangible in Nature?



Answer



This is all about potential; it is common that a particle movement is described by a following ODE:
$m\ddot{\vec{x}}=-\nabla V(\vec{x})$,


where $V$ is some function; usually one is interested in minima of $V$ (they correspond to some stable equilibrium states). Now, however complex $V$ generally is, its minima locally looks pretty much like some quadratic forms, and so the common assumption that $V(x)=Ax^2$... this makes the last equation simplify to:



$\ddot{x}=-\omega^2x$,


with solution in harmonic oscillations.


The common analogy of this is a ball in a paraboloid dish resembling potential shape; it oscillates near the bottom.


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