The law of the pendulum, discovered by Galileo Galilei, states that swinging objects follow the same path and have a period between swings that remains constant. Galileo attracted immediate attention for the discovery, which was later used in clock regulation.
The study of the pendulum and its behavior set the groundwork for much of Sir Isaac Newton's scientific work in the study of physics. Galileo understood that air resistance over time slows and eventually halts the pendulum's swing, but he proposed that, under ideal conditions, the pendulum continues its swing with the same pattern. The length of the string or chain of the pendulum determines the period of swing, with longer strings having longer periods. The pendulum at rest is said to be in a state of equilibrium.