来自《耶鲁大学开放课程：基础物理 第8集 第8集》

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  and that's going to be L^2 / 2.
  它将等于 L^2 / 2
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  So, if you do that you'll get L / 2.
  所以最后的结果就是 L / 2
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  I'm not doing every step in the calculus
  计算的具体过程我就不细写了
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  because at this point we should be able to do this without every detail.
  因为到现在我们应该不用再一步一步细讲了
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  So, the center of mass of this rod,
  那么这个棍子的质心
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  to nobody's surprise, is right in the midpoint,
  不出所料 正好就在它的中点
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  but it assumes that the rod is uniform,
  但是这里是假定棍子是均匀的
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  whereas like a baseball bat,
  而像棒球棒
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  thicker at one end and thinner at the other end,
  一头粗 另一头细
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  of course no one is saying that,
  当然没有人会讨论它
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  but we have assumed the mass per unit length,
  但我们已经假定单位长度的质量
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  namely M or this is a fixed number,
  也就是 M 或者这一项是个确定的数值