Figure 17-14(b)and(c) shows the transient response of a stable and an unstable respectively,
servo system responding to a step input command.
17-14(a) shows the step input command,
which is a constant input voltage applied at time t 0 to produce a desired output.
Observe that even though the stable system exhibits overshoot.
the output oscillation quickly dampens as it approaches the steady desired value.
The unstable system is one that depicts repeated un damped oscillations,
and thus the desired steady state output value is not achieved.