来自《耶鲁大学开放课程：基础物理 第4集 第4集》

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  it's proportional to sin(t)
  它正比于 sin(t)
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  and a t = 0, that vanishes, that's correct;
  那么 t = 0 时刻速度为 0 这是对的
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  you pulled it and you let it go.
  你拉弹簧并松手
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  So, the instant you released it, it had no velocity.
  在你释放物体的瞬间 物体是没有速度的
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  And it satisfies Newton's Laws, and that's your answer.
  这满足牛顿定律 且就是你要的结果
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  I want to do this simple example in totality
  我完整地做了这个简单的例子
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  because this is the paradigm.
  因为它是一个范例
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  This is the example after which everything else is modeled.
  这是一个最基础的例子
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  Pardon me?
  请再说一遍
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  You mean like t = 0, if the answer was sin(t),
  如果答案是 sin(t) 你需要 t = 0
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  where sin (t) vanishes at t = 0.
  当 t = 0 时 sin(t) 为 0
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  And cos(t), it doesn't vanish, has a robust value of 1.
  而 cos(t) 不为 0 它有一个确切的值 1