[物理] inelastic collision & ke

Actually, the term "inelastic" means, in physics, that the energy gathered by an object from impact is not completely transformed into "elastic potential energy" under the compression arising from the impact. This is how the term "inelastic" comes.

As such, the energy restored from the compression (i.e. the elastic potential energy) is less than the original kinetic energy of the system before collision. This is why there is a loss of kinetic energy during an inelastic collision. The lost energy commonly goes in the form of heat and, sometimes, sound.