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 is a b, there is an x from there,
  还有一项是 b 这里的 x 源于上式
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  and another x,
  还有一个 x
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  because you have to multiply this by the x coordinate of this thing,
  因为这一项必须乘以 x 坐标才行
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  because that's the coordinate of the center of mass of this.
  因为它等于物体的质心
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  There are two xs, that's what you've got to remember.
  这里有两个 x 你们必须要记住
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  So, that should be integrated from 0 to h,
  那么 积分限是从 0 到 h
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  that'll give me h^3 / 3.
  积分项的结果是 h^3 / 3
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  So, I get 2·M·b·h^3 / 3A·h.
  那么得到的结果就是 2·M·b·h^3 / 3A·h
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  Now, you know there is one more thing we have to do.
  现在 我们还得完成另外一项任务
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  We must replace the area of the triangle
  我们要把三角形的面积
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  by one half base times altitude, which is b·h.
  换成二分之一的底乘以高 也就是 b·h
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  I also forgot to divide everything by the mass,
  我忘了除以质量了