RESONANCE RESPONSE OF A MODERATELY DRIVEN RIGID PLANAR PENDULUM

The steady-state motion of a rigid planar pendulum has been studied as the drive frequency was tuned through ''resonance'' of the pendulum. Depending on amplitude of the drive, dramatically different responses were observed. The only motions studied in detail were ones involving period-one limit cycles. A range of surprisingly large hysteresis was discovered, in which amplitude jumps occur in only one direction. A hi ghly nonlinear mode, that is not chaotic, was discovered. It is appare ntly known by bell ringers but not by physicists. Amplitude jumps out of the bell-ringer mode appear to exhibit transient chaos for some cas es. (C) 1996 American Association of Physics Teachers.