A vibration is the motion of a body or system of connected bodies that oscillates about a position of equilibrium. In general, there are two types of vibration, free and forced. When the motion is maintained by the restoring forces only, the vibration is said to be a free vibration. When a periodic force is applied to the system, the resulting motions are described as a forced vibration. Free and forced vibrations may be either damped or undamped. When the effects of internal or external friction may be neglected, the vibration is said to be undamped free vibration. However, all vibrations are actually damped to some degree. The amplitude of the damped free vibration slowly decreases until, after a certain time, the ...