来自《耶鲁大学开放课程：基础物理第8集第8集》

So, if you have a pistol -- you manufactured a pistol --

如果你有一支手枪假如你生产手枪
the bullet's coming out of the pistol at a certain speed,

一颗子弹以某个速度射出手枪
and you want to tell the customer

你想告诉顾客
what the speed is. How do you find it?

子弹的速度是多少如何来求呢
Well, nowadays we can measure these things

现在我们可以测量这些量
phenomenally well with all kinds of fancy techniques,

应用许多奇妙的技术使测量很精确
down to 10^(-10) seconds.

甚至能精确到到 10^(-10)秒
In the old days, this is the trick people had.

在过去人们用的就是这种方法
You go and hang a chunk of wood from the ceiling.

在天花板上悬挂一块木头
Then, you fire the bullet

然后你射出子弹
with some speed v0 and you know its mass exactly.

其速度是 v0 你知道子弹的精确质量
The bullet comes, rams into this chunk.

子弹射过来射入摆中