有關能量的一條問題。。。。。。。。

You need to be aware that "force"(力) is different from "energy"(能量). When a force does work on an object, energy is produced (or more exactly, energy is transferred from the force to the object).

In the situation that the two balls come to rest after a head-on collision, there are forces acting on each ball to bring them to stop. Since each of the force acts in opposite direction to the motion of the ball, it (the force) does negative work onto the ball. In contrary to doing positive work by a force to produce energy on the object, negative work releases energy from the object. Thus the original kinetic energy of the two objects will be transferred to heat energy after the collision. There is no energy destruction by the law of conservation of energy.

根據能量守恆定律，能量不會消失，只會轉換成不同的形式
所以如果兩個球撞擊之後就停止左，咁能量一定轉左做其他野，可能系勢能(正常現實基本上唔會遇到)，可能系聲能,熱能或光能