Once they start moving,

一旦它们开始移动
it's like a pendulum

它们就成为了一个摆
with the initial momentum, or energy.

具有初动量或者说能量
It can climb up to the top and convert the potential to kinetic,

它可以荡到最高点将势能转化为动能
or kinetic to potential.

或是动能转化为势能
There is no loss of energy in that process.

在这个过程中没有能量损失
Therefore, if you extract this velocity

因此如果你解出这个速度
and took (1 / 2) times this velocity squared,

取这个速度平方的 1 / 2
you may in fact equate that to g·h.

你就可以令它与 g·h 相等
So, let me summarize this last result.

让我总结出最后这个结论
In every collision,

在每个碰撞过程中
no matter what, momentum is conserved;

无论如何动量都是守恒的