Forced Vibration of S.D.O.F System
Forced vibration is the one in which external energy is added to the vibrating system. The amplitude of a forced-undamped vibration would increase over time until the mechanism was destroyed. The amplitude of a forced-damped vibration will settle to some value where the energy loss per cycle is exactly balanced by the energy gained.
Examples of this type of vibration include a structure subjected to vibrating machines, vibration of a building during an earthquake or under the action of wind, etc.
To understand the behavior of the single degree of freedom system when time varying force i.e ground motion is applied.