A mass *m* is situated at the end of a spring of (unstretched)
length *L _{0}* and negligible mass. The spring is fixed at
the other end and the motion is restricted to two spatial dimensions in
a vertical plane, with the y-axis representing the vertical (if gravity
is switched on).

We use Hooke's law (with spring constant *k*) for the spring force,
and include a damping term that is proportional to the velocity of the
mass. You can also choose for the spring to behave like a spring only
when stretched, and have no effect when compressed (i.e. it is more like
a string).

Applying Newton's Second Law yields a second-order ordinary differential equation, which we solve numerically in the simulation and visualise the results.