Well, you might say, "Look, we already did this last week,

你们可能会说 "上周我们已经学过了
when I studied the Solar System,

我们不是研究过太阳系嘛
where there are planets moving around the Sun

行星围绕太阳运动
so that makes at least two bodies, the Sun and the planet."

那么这就会至少涉及两个物体太阳和行星"
But actually,

但实际上
the Sun was not doing anything interesting in our analysis.

太阳在我们所关心的分析中并不起作用
The Sun just stood there as a source of the gravitational force.

太阳仅仅待在那儿作为一个引力源
It's the planet that did all the orbiting

而真正在做轨道运动的是行星
and that was the problem in two dimensions,

而且这是一个二维问题
but of only one body.

仅涉及一个物体
So now, we are going to enlarge our domain

现在我们要把研究领域扩大到
to more than one body obeying Newton's Laws.

遵守牛顿定律的多体运动