Restoring force
= Restoring force
{title2=$F(x)=-kx$}
{wiki}
A restoring force acts toward an <equilibrium> when a body is displaced from it. In one dimension, taking <displacement> $x=0$ at <equilibrium>, this means $xF(x)<0$ for sufficiently small nonzero $x$. An ideal linear <spring> has $F(x)=-kx$ with positive <spring constant> $k$, producing <simple harmonic motion> for a constant <mass> without <damping>. More general restoring forces need not be linear.