来自《耶鲁大学开放课程：基础物理 第8集 第8集》

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  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
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  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
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  It's the planet that did all the orbiting
  而真正在做轨道运动的是行星
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  and that was the problem in two dimensions,
  而且这是一个二维问题
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  but of only one body.
  仅涉及一个物体
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  So now, we are going to enlarge our domain
  现在我们要把研究领域扩大到
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  to more than one body obeying Newton's Laws.
  遵守牛顿定律的多体运动
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  So, let me start with the simplest possible case:
  让我们以最简单的问题开始
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  two bodies.
  二体问题
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  And I will again start with the simplest case of
  而且我将再次以一维的运动来
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  their moving in one dimension;
  作为出发点研究这个最简单的例子
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  then, we'll put in more.
  然后我们再研究多维运动