来自《耶鲁大学开放课程：基础物理 第7集 第7集》

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  So, today we're going to make a big leap,
  今天我们来做一次大的跳跃
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  because today you're going to understand
  因为你们将学习
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  how planets move around the Sun.
  行星如何绕着太阳运动
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  That's a mega problem, right?
  这是一个大问题 对吧
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  The little ms you put in the equation
  你列在方程里的 m
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  are not mass of a pulley or a plane,
  不再是滑轮或者斜面的质量
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  but mass of Jupiter or mass of the Sun.
  而是木星或者太阳的质量
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  So, you're doing something of cosmological proportions.
  你们在做宇宙量级的事情
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  And you don't need to know too much more to do that.
  你们已有的知识基本足够做这样的问题了
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  You're almost there.
  你们差不多都会了
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  So, I'm going to just tell you the one missing thing.
  只还差一件事 现在我就要告诉你们
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  So, what Newton had done is to realize that
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