When two hard solid objects collide, acoustic waves are generated at the point of impact. The deformation of the objects and their subsequent separation are associated with the propagation of these acoustic waves through the objects and their reflection from the surfaces. In this paper we follow the time development of these processes in detail for one-dimensional collisions involving Hooke's law springs. We calculate the degree of inelasticity of the collision from the state of internal excitation of the springs after separation occurs. An attempt is made to generalize the conclusions obtained in this one-dimensional model to the qualitative description of the collision of hard spheres.