来自《耶鲁大学开放课程：基础物理 第9集 第9集》

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  there'll be some α,
  就有某个 α
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  and this thing called torque is I·α.
  而转矩这个物理量就等于 I·α
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  Now, I think it's very clear
  我想现在应该很显然了
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  that if I had several forces acting on the body,
  如果有几个力作用于该物体
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  then the torque will be ∑ (Fi·Ri),
  那力矩就应为 ∑ (Fi·Ri)
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  and there's just one final caveat to this thing,
  运用这个公式时只有一个重要提醒
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  one final qualification,
  最后一个限定条件
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  which is that, in practice,
  那就是 在实际情况中
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  the forces that are used to rotate a body
  这些令物体旋转的外力
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  may not always be perpendicular.
  可能不总是垂直的
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  You can apply a force in some other direction,
  你可以在其他方向上施以外力
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  like that.
  比如这样