We are defining a pendulum as any object that oscillates back-and-forth on a rope of stiff arm without any outside forces pushing or slowing it down.

The pendulum has an anatomy. The, "arm," is a piece, either a rope or rod, that attaches the mass at the end to the pivot point at the other end. The length of the rod is measured from the pivot point to the center of mass of the object on the end. The "bob" is the name given to the mass attached to the end of the arm. To count at simple harmonic motion the amplitudes of the swinging should be the same and the angle should be less than 10°. The "period" of motion is the time for the bob to travel back-and-forth, measured in seconds. The "amplitude" is the sideways distance the bob is pulled.

We will take some liberties when solving real world problems by assuming all the amplitudes are the same even when the pendulum looses a small amount of amplitude with each oscillation.

• T: the period of motion measured in seconds
• L: length of the pendulum's arm in meters
• g: the acceleration due to gravity in ^m/_s².