来自《耶鲁大学开放课程：基础物理 第8集 第8集》

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  There are no horizontal forces.
  没有其它水平方向的力
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  If you move, everything else has to move.
  所以如果你移动 别的物体也会移动
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  So, what'll happen is that, when you move,
  所以将要发生的就是 当你移动时
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  the boat will have moved from there
  船将运动到这里
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  maybe somewhere over to the right like this.
  可能移动到右边的这一位置
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  You are certainly at the edge of the boat,
  你显然在船首
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  but the boat has moved a little extra distance δ,
  但是船额外移动了一个距离 δ
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  and you have to find that δ.
  你要求出 δ
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  You find it by the same trick.
  你可以用相同的方法解决这个问题
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  You find the center of mass of you and the boat,
  先找到你和船的质心
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  preferably with this as the origin.
  取这一点作原点较好
• 
  
  You can use any origin you want for center of mass,
  求解质心可以取任意点作原点