Abstract: The varying regularity of oscillating period of three-wire pendulum with rigid body above it is derived theoretically according to the oscillation equation, a new experiment is designed to measure the oscillating period of three-wire pendulum in all sorts of condition, and the varying regularity is exposited intuitively using descriptive geometry solution. It is shown that the theoretical result is in agreement with the experiment.

Key words: three-wire pendulum, oscillating period, gyration radius, mass distribution