Ringdown
= Ringdown
{title2=$x(t)=Ae^{-\gamma t}\cos(\nu t+\phi)$}
Ringdown is the freely decaying motion of a <resonator> after an applied drive is removed. For an underdamped <damped harmonic oscillator>, the amplitude decays as $e^{-\gamma t}$ while the <angular frequency> is $\nu=\sqrt{\Omega^2-\gamma^2}$. In the weak-damping limit, the cycle-averaged stored <energy> decays as $e^{-2\gamma t}$, giving the <quality factor from ringdown> $Q\simeq\Omega/(2\gamma)$.