来自《耶鲁大学开放课程：基础物理 第11集 第11集》

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  it has to go along a circle with that as the radius.
  它必定沿着以这个为半径的圆运动
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  So, the momentum p will look like that,
  那么动量 p 是这样的
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  and the r measured from any point will look like this
  从任一点为起点的 r 是这样
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  r cross p, which is what I'm calling L;
  r 叉乘 p 就是我所说的 L
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  the length of L will be r cross p,
  L 的大小等于 r 叉乘 p
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  the lengthy of r cross p, which will be r.
  r 叉乘 p 就等于 r
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  For p, let me write m·v,
  p 写成 m·v
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  v is tangential velocity here.
  v 在这里是切向速率
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  But we both know that that is equal to m times ω times r
  我们都知道 p 等于 m 乘以 ω 乘以 r
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  because the tangential velocity is ω·r.
  因为切向速率为 ω·r
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  That something we did long back.
  这个我们早就知道
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  But then this becomes m·ω^2·r.
  它变成 m·ω^2·r