来自《耶鲁大学开放课程：基础物理 第1集 第1集》

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  In fact, let me go back to this equation here.
  让我们回头再看看这个方程
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  You'll put time t=0, x doesn't have this term,
  你令时间t=0 这一项就消失了
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  doesn't have this term, and it is c.
  这一项也是 只剩下常数c
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  So I realize that the constant, c,
  所以我发现常数c
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  is the initial location of the object,
  就是物体的初位移
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  and it's very common to denote that by x0.
  我们习惯用x0表示
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  So the meaning of the constant is
  常数的含义是
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  where was the object at the initial time.
  物体的初位移
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  It could've been anywhere.
  初始时可以在任何地方
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  Simply knowing the acceleration
  仅仅知道加速度是
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  is not enough to tell you where it was at the initial time.
  不足以告诉你它在初始时刻的位移的
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  You get to pick where it was at the initial time.
  你需要选取初始时刻的位移