For a mass m attached to a  spring with spring constant k
The force is proportional to the displacementx.
\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?