Summary This paper describes an impulse-based system for modeling collision/contact interactions and discusses the prospect of creating a hybrid simulator that uses both impulse and constraint-based simulation. It attempts to address the problem of how to properly model collisions of objects and rigid bodies both in simple and complex systems. Key Ideas * A purely contraint-based system has incredible difficulty handling sytems with a very large number of degrees of freedom with many collisions and very transient contact configurations. * Objects are represented as convex polyhedra and a collision is declared when the distance between two objects falls below some threshold. * When a collision is detected, the collision response subsystem computes the appropriate impulses to apply to the colliding objects. This impulse prevents interpenetration while adhering to other physical constraints, such as friction. * Constraint-based dynamics are preferred over impulse-based simulation when there is an enormous amount of collision detection needed. * A hybrid simulation model combining impulse- and contraint-based simulation could be used to handle complex systems by predetermining which types of contact interaction would be processed by impulses and which by constraints.