来自《耶鲁大学开放课程：基础物理 第7集 第7集》

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  in which here's the Earth and here's the apple --
  这里有个地球 这是个苹果
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  there's an m sitting there --
  这放一个 m
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  but imagine the apple's getting bigger and bigger;
  假设这个苹果变得越来越大
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  the formula's not going to change.
  公式不会改变
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  Make it bigger and bigger and bigger, and bigger,
  苹果越来越大 越来越大
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  till it looks like the apple is that big
  直到它像这么大
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  and the Earth is that big.
  而地球那么大
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  Then, you will have to agree that
  那么你们得承认
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  from that point of view
  从这点来讲
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  you should also have the mass of the Earth here,
  地球的质量也应该被囊括在内
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  playing a symmetric role.
  作为一个对称的角色
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  So, these two masses have to be there.
  所以这两个质量必须要在这里