Book: # 5

THE PROCEDURE: A wilberforce pendulum is a pendulum that hangs from a spring. The moment of inertia of the pendulum bob is adjusted so that the rotational frequency is approximately equal to the transitional frequency. This pendulum has two degrees of freedom. The system is started by pulling downward on the mass. When the system is adjusted properly the energy of the pendulum flows back and forth between the two modes, transitional and rotational. The two normal modes have almost equal frequencies, so the beat frequency between the normal modes is much less than the average frequency of the two modes. For this reason the exchange of energy between the two degrees is slow enough to be easily observed.