来自《耶鲁大学开放课程：基础物理 第7集 第7集》

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  then, you will get the same answer as the person using this formula.
  就得到这个公式了
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  So, that's very important to understand
  这部分内容很重要
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  how these two are saying the same thing.
  要理解这两个表达讲的是同样的事
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  It is best understood in terms of the graph that I've drawn for you.
  这是对我画的那幅图的最好理解
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  You shift your origin to one place
  你将坐标原点改到另一个位置
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  and you also shift the zero potential to one place.
  与此同时 零势点也改了位置
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  Now, for a circular orbit, what's the energy?
  对于圆周轨道来说 能量等于什么
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  It's (1/2)·m·v^2 - G·M·m / r.
  等于 (1/2)·m·v^2 - G·M·m / r
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  But we know that (1/2)·m·v^2 is v^2
  我们知道 (1/2)·m·v^2 这里是 v 的平方
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  and m·v^2 is a centrifugal force,
  而 m·v^2 是离心力
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  I mean the centripetal force.
  我是指向心力
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  So therefore, you can write that as
  因此你能写成