来自《耶鲁大学开放课程：基础物理 第8集 第8集》

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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
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  because the center of mass is this weighted average
  因为质心是加权平均值
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  divided by the total mass,
  要除以总质量
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  so I've got to divide by M.
  所以我要给等式除以 M
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  Well, I claim, if you do this and cancel everything
  我来告诉你们 如果你这么算 把这些都约掉
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  you will get the answer of (2 / 3)·h.
  结果就是 (2 / 3)·h