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, it is again here that Newton decided
  牛顿认为
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  that the force that bends the planets around the Sun
  使得行星绕着太阳转的力
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  is the same as the force that bends the Moon around the Earth.
  和使得月亮绕着地球转的力是一样的
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  It was known by then the Moon's also going around the Earth.
  那个时候已经知道月球也绕着地球转
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  So, let's look at that problem.
  让我们来看看这个问题
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  So, here's the Earth, and here is the Moon,
  这是地球 这是月球
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  and it's going around the Earth.
  月球绕着地球转
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  Now, the Moon is accelerating towards the Earth
  月球朝着地球作变速运动
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  and that's something we have learned in this course.
  我们在这门课里面已经讲过这个
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  Then, here is the famous apple,
  这是那个著名的苹果
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  also accelerating towards the Earth.
  也朝着地球加速运动
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  And Newton decided that the cause behind both the forces
  牛顿认为这两个力背后的原因