This document discusses momentum and impulse. It defines momentum as the product of an object's mass and velocity, and notes that momentum allows analysis based on these properties rather than just force and acceleration. Impulse is defined as the product of the magnitude of a force and the time interval it acts. It also discusses the law of conservation of momentum, which states that the total momentum of a system remains constant during an elastic collision or any other interaction where the net external force is zero. Perfectly elastic and inelastic collisions are described.