Elastic and inelastic collisions

A perfectly elastic collision is defined as one in which there is a no total loss of kinetic energy in the collision. An inelastic collision is one in which part of the kinetic energy is changed to some other form of energy in the collision. Any macroscopic collision between objects will convert some of the kinetic energy into internal energy and other forms of energy, so no large-scale impacts are perfectly elastic. Momentum is conserved in inelastic collisions, but you are unable to track the kinetic energy through the collision since some of it is converted to other forms of energy. Collisions in ideal gases approach perfectly elastic collisions, as do scattering interactions of sub-atomic particles, which are deflected by the electromagnetic force. Some larger-scale interactions like the slingshot type gravitational interactions between satellites and planets are perfectly elastic. Collisions between hard spheres may be nearly elastic, so it is useful to calculate the limiting case of an elastic collision. The assumption of conservation of momentum as well as the conservation of kinetic energy makes it possible to calculate the final velocities in two-body collisions. (University of Waterloo, 2010)