Harmonic potential ($V(x)=\frac{1}{2}k{x}^2$)

A quadratic potential energy about a stable equilibrium. In one dimension $k>0$ is the restoring stiffness and the force is $-dV/dx=-kx$. A mass $m$ undergoing undamped motion has angular frequency $\sqrt{k/m}$. A smooth potential with a nondegenerate local minimum is approximately harmonic for sufficiently small displacements; higher-order terms describe departures from simple harmonic motion.