The specifics of a question I am working on are, "After a 0.280-kg rubber ball is dropped from a height of 1.80 m, it bounces off a concrete floor and rebounds to a height of 1.45 m."
Why doesn't the ball return to the same height?
The ball is deformed while bouncing off. In theory, this can be modelled as an entirely elastic process as a relatively good approximation, however, it actually is not, as some energy is lost in the process and radiated away as heat (try deforming a ball a few hundred times, it will heat up).
The process is therefore not entirely elastic, which reduces the kinetic energy of the ball.
Additionally, a number of other forces affect the ball, listing those mentioned above again for completenes and ordered roughly by the magnitude of the effect: