Rigid body simulation for 3D character animation

Martin Kleppmann

Implementation notes for Newton's cradle

Newton's cradle is modelled as five spherical bodies, each with its centre of mass at the centre of the ball (i.e. the wire connecting it to the frame is assumed to be massless). The joint to the frame is modelled as a 'nail' constraint, and the frame itself does not exist in the simulation. Collision detection is performed not on the basis of the meshes (since these are polyhedral approximations and not exact spheres), but using a special type of sphere/sphere constraint which computes its behaviour using the positions of the centres of the balls and their radii.

For the simulation to work accurately, a very low penetration tolerance must be set. The different examples are simulated in exactly the same way, independent of the number of balls moving or the elasticity of collisions.

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