来自《耶鲁大学开放课程：基础物理 第7集 第7集》

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  and when you go from start to finish
  从起点到终点的总改变量
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  the total change will in fact be the change in U, from start to finish,
  就是 U 从起点到终点的改变量
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  and won't depend on how you got there.
  和路径无关
• 
  
  So basically, what you're doing is,
  所以基本上来说 你们要做的就是
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  in the xy plane
  在 xy 坐标系
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  you are defining a function U of xy,
  定义一个关于 x 和 y 的函数 U
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  which is like a height.
  类似于高度
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  You defined the force in a clever way
  你们可以巧妙地定义力
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  so that F·dr is the change in the height, as you march.
  使得 F·dr 是行进中高度的改变量
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  So, you can start at any point on the mountain,
  那么 你们可以从山上任意一点开始
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  go to any other point on the mountain;
  移动到另外一个点
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  if you're only keeping track of the change in height
  如果只考虑高度的改变