The interactions between a robot and its environment involving sudden contact and impact comprise the key elements of impulsive manipulation. Of the collision models in use in robotics to date no one model is able to capture the richness of impulsive manipulation in impact and grasping analysis. Thus, we introduce an algebraic collision law specifically tailored to robotic interactions such as grasping. Synthesizing an algebraic collision law given in other arenas with the operational contact inertia matrix, we obtain an impulsive manipulation model which is consistent with the laws of physics and also computationally efficient. This law has potential uses in many aspects of dynamic simulation and manipulation.