And I have purposely made the arrow shorter to indicate that it has been slowed because we are going to argue its mass didn't change, so the only way to change its energy is to change its velocity.

我已经故意将这个箭头弄短,用来象征它变慢了,因为我们将证明它的质量没有变，只有它的能量改变了,也就是它的速度变了。

麻省理工公开课 - 固态化学导论课程节选