Definition:Forced Vibration/Forcing Frequency

Definition
Consider a second order ODE in the form:
 * $\dfrac {\d^2 x} {\d t^2} + 2 b \dfrac {\d x} {\d t} + a^2 x = K \cos \omega x$

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

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

The frequency:
 * $\dfrac \omega {2 \pi}$

is known as the forcing frequency of $S$.

Also known as
Some sources give this as the impressed frequency.