来自《耶鲁大学开放课程：基础物理 第10集 第10集》

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  I can tell you how fast the car is moving.
  就能算出车的速度
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  If I tell you how fast the car is moving,
  如果知道车的速度
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  I know the rate at which the wheels are spinning,
  就能知道车轮的转速
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  provided it's not skidding.
  前提是车轮不打滑
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  If it's skidding, these bets are off.
  要是车轮打滑 这些计算就没什么意义了
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  All right, so now we continue with this saga of rotations.
  好 我们继续来讲转动
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  And let me remind you where we stand.
  讲到哪我提醒你们下
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  When I did F=m·a after telling you a little bit about
  在我跟你们讲完如何测质量之后
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  how mass is measured,
  写下 F=m·a 时
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  and everybody knew how acceleration is measured,
  大家都想知道加速度是怎么测的
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  what did we do?
  我们当时是怎么做的
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  We first took a bunch of problems
  我们先是做了一些