For a mass m attached to a  spring with spring constant k
The force is proportional to the displacement$x$.
$\vec{F}=-k*x$
Assume there is a damping force which is proportional to the velocity
$F=m\frac{d^2m}{dt^2}=-k*x-b*v$
The above equation can be rewrite as $m\frac{d^2m}{dt^2}+b \frac{dx}{dt}+k*x=0$

Do you notice the similarity between equation for spring and pendulum set?