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, there is no universal symbol for all those things.
  所以对所有这些 没有普适的符号
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  I will write it in the simple case
  我写一种最简单的情况
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  where we imagine at the center some massive object, like the Sun,
  设想中心是个大质量物体 比如太阳
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  and something tiny going around it,
  围绕周围的是些很小的物体
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  and the center of coordinates is chosen
  坐标轴的中心就取为
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  to be at the center of the massive object.
  巨大质量物体的中心
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  This is the force on the little guy.
  这就是那个小物体受到的力
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  This is the Law of Gravity.
  这就是引力定律
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  It's called the Law of Universal Gravitation
  称为万有引力定律
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  because it really is universal.
  因为这定律真的是万用的
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  You got to realize that.
  你得承认
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  It's a tremendous leap of faith
  这是一次信仰的巨大飞跃