Abstract: Apparatus for modelling or simulating the dynamics of interacting rigid bodies. In the apparatus, the rigid bodies are represented as convex polyhedra. Contacts between the bodies are modelled as contacts between a face and a vertex or between edges. All other types of contact are reduced to these types. The beginning or end of a contact is determined by means of linear interpolation. The dynamics of the contacts are modelled as contacts between massless rigid surface elements which are connected by massless viscous layers to the objects. The viscous layer connecting a surface element to its object permits the surface element to move either perpendicular to or tangent to the plane of contact. The properties of the viscous layers determine the dynamics of the contacts. In the implementation, the properties are described by means of two systems of springs and dampers, one permitting motion in the perpendicular direction and the other motion in the tangential direction.