And of course this has a slight thickness,

当然现实中它肯定会有一点厚度
because anything you make of matter has some thickness,

因为无论什么物质做的东西都会有厚度
at least one atom thick,

至少一个原子的厚度
but imagine that thickness is negligible,

假设这个厚度是可忽略的
so it's like a piece of metal,

所以它就像一块金属
a piece of foil or something, but it's rigid,

一块金属箔或者别的什么而且还是刚体
and this is the rigid body we're going to study.

这就是我们要研究的刚体
This rigid body can move in the plane of the blackboard and rotate,

这个刚体可以在黑板平面内移动和旋转
but we're going to grab it at one point.

但我们要固定住一点
So, let's pick some point, here.

我们随便取一个点这个点
If I grab it at that point and I ask you,

如果我固定住这一点然后问你
"What can this fellow do?"

"现在它会怎么运动"