ABSTRACT
We begin an important section, for the nature of the response to sinusoidal forcing is quite different from anything so far considered.
In all previous cases, whether of free vibrations or of response to sudden forces of simple form, the vibration occurs at the natural frequency of the system. The vibration also dies away due to damping and we are left with zero displacement in all cases except those in which a constant force remains, in which case the final displacement is none other than the static displacement due to that force.
