The damping ratio zeta of a critically damped second-order system is:

Explanation

In a second-order control system, the damping ratio ζ (zeta) defines system transient behavior: ζ = 0 (undamped), 0 < ζ < 1 (underdamped), ζ = 1 (critically damped - fastest response without overshoot), and ζ > 1 (overdamped).