Pendulum With a Rotational Vibration

This work involves a pendulum made up of a mass, a pivoted weightless rod, and a spring. The mass is constrained to maintain its axial position on the rod, but is allowed to move rotationally on the rod under the influence of the spring. The pivot is vibrated rotationally at a high frequency about a vertical axis. It is found that, in some conditions, the vibration causes new stable equilibrium positions.