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A computer aided dynamic and design sensitivity analysis technique for planar dynamic systems undergoing intermittent motion is developed and applied. Planar dynamic systems made up of multiple rigid bodies connected by joints and force elements are modeled. A constrained dynamic system approach that accounts for discontinuous velocities associated with impulsive loading and impact between bodies is developed. A new numerical integration technique for mixed differential and algebraic equations that automatically defines and integrates for independent generalized coordinates has been developed. It has demonstrated an order of magnitude improvement in computing efficiency compared to preceding techniques. Intermittent motion dynamic effects due to impulsive loading or impact have been incorporated into the dynamic simulation, using a pieced interval dynamic analysis technique in which momentum balance relations are used to determine discontinuities in velocity at logical event times. This technique has been demonstrated on multibody, multiple contact point applications in mechanisms and automatic weapons. To assist in design optimization of mechanical system dynamics an adjoint variable design sensitivity analysis technique has been developed for calculation of first and second order derivatives of dynamic response with respect to design. Numerical calculations have demonstrated that accurate first and second derivatives can be obtained for moderate scale dynamic systems. (Author)