来自《耶鲁大学开放课程：基础物理 第2集 第2集》

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  If you say, "Where is time?"
  如果你说 "时间在哪"
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  One way to mark time is
  标记时间的一种方法是
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  to imagine it carries a clock as it moves,
  想像它带着时钟运动
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  and put markers every second.
  并且每秒做一次标记
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  That may be t=0, t=1, t=2 and so on.
  也就是 t=0 t=1 t=2 等等
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  So, time is measured as a parameter along the motion of the particle.
  这样 时间就被记为质点运动的一个参数
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  It is not explicitly shown.
  它没有直接被表示出来
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  but you can sort of tell that the particle is moving slowly or rapidly
  但你可以通过观察计时点之间的距离
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  by looking at the space in between these tick marks.
  来判断该物体运动的快慢
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  For example, here, in one second it went from here to here.
  例如 在一秒内它从这儿运动到这儿
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  Here, in one second, it seems to have gone much further,
  在这一秒内 它似乎运动了更远的距离
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  so it's probably traveling faster.
  所以这段时间它可能运动得更快