Or there may be an inelastic collision, when the photon hits an atom and knocks out an electron—the old photoelectric effect.
|inelastic collision |
A collision between bodies in which the total kinetic energy of the bodies is not conserved. In an inelastic collision, the total momentum of the two bodies remains the same, but some of the initial kinetic energy is transformed into heat energy internal to the bodies, used up in deforming the bodies, or radiated away in some other fashion. Inelastic collisions, such as the collision of two balls of clay, tend to result in the slowing and sometimes the joining together of the colliding bodies. Comapre elastic collision.