Pendulums

About

"In mech., a body so suspended from a fixed point as to move to and fro by the alternate action of gravity and its acquired energy of motion. The time occupied by a single oscillation or swing is counted from the time of the descent of the pendulum from the highest point on one side till it attains the highest point on the opposite side. This time is called the period of oscillation of the pendulum. A simple pendulum in the mechanical sense is a material particle suspended by a weightless rod and moving without friction. A single weight attached by a string, etc., approximates to an ideal simple pendulum."

--from the Century Dictionary definition for pendulum