Introduction to Vibrations
Vibration can be regarded as a subset of dynamics, in which a system subjected to restoring forces oscillates about an equilibrium position. The restoring forces are due to elasticity or gravity. Two different types of excitations cause a system to vibrate: initial excitation and external excitation. The vibration of a system caused by non-zero initial excitations, including initial displacements or initial velocities (or both), is known as free vibration. The vibration of a system caused by externally applied forces is known as forced vibration.