来自《耶鲁大学开放课程：新生有机化学 第3集 第3集》

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  Now let's just think about that a little bit.
  那让我们进一步深入
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  Suppose you look at the line density here.
  让我们观察下图中所示的场力线密度
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  Through that little line, there are three lines of force that pass.
  由图可知三条场力线通过了那条蓝线
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  So let's say that means there are three, the force is three at that--
  那我们就姑且将这个力定义为三级
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  and it's obviously pointing to the right. Okay?
  很明显力的方向是指向右方的
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  Now suppose you checked it out at that distance.
  若我们把那蓝线移到现在这个距离
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  Stronger force or weaker force?
  那么力变小了还是变大了
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  Weaker force.
  变小了
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  Weaker.
  没错 变小了
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  In fact only one or one and a half, or something like that,
  因为此时大概只有一条或一条半场力线
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  lines of force are going through that.
  通过了蓝线
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  Now, how does it depend on distance,
  那么力和距离的关系究竟是怎样的