Definition:Forced Vibration

Definition
Consider a physical system $S$ whose behaviour can be described with the second order ODE in the form:
 * $(1): \quad \dfrac {\mathrm d^2 x} {\mathrm d t^2} + 2 b \dfrac {\mathrm d x} {\mathrm d t} + a^2 x = K \cos \omega x$

for $a, b \in \R_{>0}$.

Let $b < a$, so as to make $S$ underdamped.

Then the steady-state motion of $S$ is referred to as forced vibration of $S$.