Physical modelling is a way of describing the behavior of an object
in terms of the interactions of external and internal forces.
Simple methods for describing motion usually resort to having the object
follow a pre-determined trajectory.
Physical modelling, on the other hand, is about dynamics.
Physically based modelling methods will tell show us how a table-cloth
will drape over a table or how a curtain will fall from a window.
A common method for approximating such nonrigid objects is as a network
of points with flexible connections between them.