来自《耶鲁大学开放课程：基础物理 第8集 第8集》

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  to find the center of mass of this triangle
  如何来寻找这个三角形物体的质心
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  I can divide it into vertical
  我可以将它分解成为
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  strips which are parallel to each other,
  与坐标轴垂直且相互平行的小窄条
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  and find the center of mass by adding
  然后将所有小窄条的质量进行加权平均
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  the weighted average of all these things.
  来确定物体的质心
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  For that, I need to know what's the mass of the shaded region.
  要做到这一点 我要知道各小窄条的质量
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  So, let's call it δm.
  我们将其记为 δm
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  The mass of the shaded region is the mass per unit area.
  每个小窄条的质量用单位面积的质量表示
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  I'll find the area later on in terms of b and h,
  我会通过 b 和 h 来计算面积
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  but this is mass per unit area.
  但这里的质量是单位面积上的质量
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  Then, I need to know the area of the strip.
  然后 我需要知道小窄条的面积
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  I'm going to give the answer
  我会直接给出答案