# Non-linear dynamics problem: A mechanical analog of dx/dt=sinx [closed]

I have been stuck at this particular problem for a while.This is a problem from Nonlinear Dynamics And Chaos by Strogatz.

The thing I am having hard time finding a mechanical system following dx/dt=sinx even approximately. No, simple harmonic motion doesn't work.

Then, the problem asks to intuitively explain why x=0 and x=pi are stable and unstable fixed points respectively. So, it seems like the system would be 'familiar'.But, I am not finding any 'familiar' system of this equation of motion.

## closed as off-topic by Kyle Kanos, Jon Custer, John Rennie, stafusa, heatherNov 13 '17 at 21:29

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It looks like a typo to me: the equation is $\ddot{x}=\sin x$ and this is just a pendulum with a slightly odd convention for the angle. Posit $x = \pi + \theta$ and you get the usual $\ddot{\theta}+\sin\theta = 0$.