来自《耶鲁大学开放课程：基础物理 第7集 第7集》

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  we are studying something fairly general.
  我们研究的是相当平常的东西
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  So, today I go to one of the famous conservative problems
  今天我要讲到著名的守恒问题之一
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  which is the gravitational interaction.
  引力相互作用
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  So, the situation was as follows at Newton's time.
  在牛顿时代情形是这样的
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  You know that Copernicus proposed that
  你们知道哥白尼提出的
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  the way to think about our Solar System is
  描述我们的太阳系的方法是
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  to put the Sun at the center.
  假定太阳在中心
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  Now, so here is Copernicus' picture.
  这就是哥白尼的图景
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  Here's the Sun, here are the various planets.
  这里是太阳 这里是各行星
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  You have to agree that's very remarkable. Okay?
  你们应当承认这是非常伟大的 是吗
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  First of all,
  首先
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  it's remarkable because that was the period when you--
  它伟大是因为那个时代