When a particle of mass m moves on the x-axis in a potential of the form V(x) = Kx2 it performs simple harmonic motion. The corresponding time period is proportional to as can be seen easily using dimensional analysis. However, the motion of a particle can be periodic even when its potential energy increases on both sides of x = 0 in a way different from Kx2 and its total energy is such that the particle does not escape to infinity. Consider a particle of mass m moving on the x-axis. Its potential energy is V(x) = αx4(α>0) for ∣X∣ near the origin and becomes a constant equal to V0 for ∣X∣≥X0 (see figure).
The acceleration of this particle for ∣X∣>X0 is