来自《耶鲁大学开放课程：基础物理 第8集 第8集》

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  I don't want to go into the rocket problem in any detail.
  我不想详细地讨论火箭的问题
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  It's good for you to know how these things are done.
  你们知道它的原理是有好处的
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  Here's a rocket whose mass at this instant is M,
  这是一个火箭 它在这一瞬间的质量为 M
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  whose velocity is v right now.
  并且速度为 v
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  What rockets do is they emit gasses,
  火箭喷射气体
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  and the gasses have a certain exhaust velocity.
  喷出的气体有一定的速度
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  That velocity is called v0.
  这个速度我们设为 v0
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  In magnitude, it's pointing away from the rocket,
  气体朝与火箭相反的方向运动
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  and it has a fixed value relative to the rocket,
  它相对火箭有一固定的速度
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  not relative to the ground.
  不是相对于地面
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  If you are riding with the rocket
  所以假如你与火箭一起飞行
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  and you look at the fumes coming out of the back,
  观察其尾部喷出的气体