Building blocks of inelastic collisions. In the left panel two particles collide to form a third particle. In the right panel a particle breaks up, forming two particles. An inelastic collision is one in which the particles coming out of the collision are not the same as the particles going into it.
Inelastic collisions conserve both total momentum and energy just as elastic collisions do.
However, unlike elastic collisions, inelastic collisions generally do not conserve the total kinetic energy of the particles, as some rest energy is generally created or destroyed. Figure 10.4 shows the fundamental building blocks of inelastic collisions. We can consider even the most complex inelastic collisions to be made up of composites of only two processes, the creation of one particle from two, and the disintegration of one particle into two. Let us consider each of these in the center of momentum frame. In both cases the single particle must be stationary in this frame since it carries the total momentum of the system, which has to be zero.