This page contains a physics demo. A number of spheres are contained within a cube and they are connected via springs. All the objects are integrated by using a third degree polynomial. The third order term of the polynomial is estimated by looking at the difference in acceleration between two consecutive frames. The simulation runs at 100fps.
Loose springs, as well as tight(er) springs are used (see the tetrahedron). By using your mouse, you can apply force to the center sphere. The left mousebutton will pull the center sphere up, while the right mousebutton will pull the center sphere down.