METASTABLE STATES OF A LOW-FREQUENCY MESODYNAMIC PENDULUM

A preliminary study has been made of the free decay of a physical pendulum whose mass is dominated by two metal bobs, and whose period can be adjusted to exceed 30 s. The decay mechanism is predominantly anelasticity from internal friction of creep. The relaxation spectrum of this creep suggests a mechanical Barkhausen effect. In surprising contrast to exponential decay at large energy, the motion at low energy and long period is characterized by repeatable metastable states. Phase is preserved in the transition between most states even though the transitions may be chaotic. There is a lowest harmonic state which is different for Pb and Cu bobs, and below which the system transitions from free decay to stochastic fluctuation-dissipation. Noise of this stochastic state is larger than electronic noise, and power spectral density plots show that it contains mixtures of subharmonics at integral multiples of 1/4 the pendulum frequency.