Impact against a mechanism composed of nearly rigid bodies is a feature of many practical machines. These systems may include mechanisms where the relative velocities at joints are initially zero and finally must vanish or they can be another type of system such as a gear train or an agglomerate of unconnected bodies where at each contact the normal component of terminal relative velocity must be separating. These two classes of multibody impact problems – mechanisms and separate bodies that are touching – are distinguished from analyses of two-body impacts by the addition of constraint equations that describe limitations on relative motion at each point of contact between bodies. These constraint equations express the linkage between separate elements. Books on dynamics typically analyze the impulsive response of systems composed of rigid bodies linked by frictionless or nondissipative pinned joints.