来自《耶鲁大学开放课程：基础物理 第6集 第6集》

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  you gain and lose kinetic and potential.
  伴随着动能与势能的得与失
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  When you come here
  当你来到这里的时候
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  your potential energy is almost your whole energy
  你的势能几乎是你所有的能量
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  but you've got a little bit of kinetic energy.
  但你还是会有少量的动能
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  That means, your roller coaster is still moving
  也就是说 过山车到这里时还是在运动
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  when it comes here with the remaining kinetic energy.
  它还带着剩余的动能
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  You can have a roller coaster whose energy is like this.
  你可以使过山车的能量始于这一点
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  This is released from rest here.
  在这里从静止开始释放
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  It is released from rest here.
  过山车在这里从静止开始释放
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  That's the total energy
  这就是总能量
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  and this total energy line looks like this.
  这条是总能量线
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  That means, if you released it here,
  这意味着 如果你从这里开始释放