Bob moves on a circular arc centered at the left pivot when swinging to the right, and on an arc centered at the right pivot when swinging to the left.

Peter Lynch
Many damped mechanical systems oscillate with increasing frequency as the amplitude decreases. One popular example is Euler’s Disk, where the point of contact rotates with increasing rapidity as the energy is dissipated. We study a simple mechanical pendulum that exhibits this behaviour…

… Read more at http://arxiv.org/pdf/1512.03700v1.pdf