来自《耶鲁大学开放课程：基础物理 第9集 第9集》

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  as it travels along some parabolic path,
  当它沿着某条抛物线运动时
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  one instant the eraser may look like this,
  在某一时刻 黑板擦可能是这样的
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  the next instant and the eraser may look like this.
  下一时刻它可能又是这样的了
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  So, we say that it is translating and rotating.
  所以 我们说它既有平动 又有转动
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  It's a non-obvious theorem that
  很多人都无法理解
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  anything the body does from one instant to the next instant
  物体在某一时间段内的任何运动
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  can be achieved by first translating it,
  都可以通过先平动
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  then doing a slight rotation
  再转动
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  to bring it to the configuration you want.
  来获得最终的状态
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  In other words, you can go from here to here by a translation,
  换句话说 从这里到这里可以先平动
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  followed by a rotation.
  接着再转动
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  Now, a translation is what we've been studying all the time,
  平移是我们之前一直在学的东西