来自《耶鲁大学开放课程：基础物理 第1集 第1集》

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  So just a dot, and the dot can move around all over space.
  就是一个点 这个点能在空间各处自由运动
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  So we're going to simplify that, too.
  所以我们就把它的运动也简化了
• 
  
  We're going to take an entity that lives along the x axis.
  我们拿一个只能沿着X轴运动的质点
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  It moves along a line.
  它就沿着这条线运动
• 
  
  So you can imagine a bead with a wire going through it
  你可以想象一个穿在绳子上的珠子
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  and the bead can only slide back and forth.
  小珠只能前后滑动
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  So, this is about the simplest thing.
  这是最简单的模型
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  I cannot reduce the number of dimensions.
  我不能再降低维数了
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  One is the lowest dimension.
  维数最小只能是1
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  I cannot make the object simpler than being just a mathematical point.
  找不到比质点更简单的模型了
• 
  
  Then, you've got to say,
  然后 也许你会问
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  "What do I have to know about this object at the initial time?
  我需要知道物体初始状态的哪些信息呢