So the velocity at any part of the curve is tangent to the curve at that point.

曲线上任意一点的速度,都在该点和曲线相切

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That's the point where velocity is 0.

也就是速度为零的点

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At any point on the graph you can take the derivative, which will be tangent to the curve at each point, and its numerical value will be what you can call the instantaneous velocity of that point and you can take the derivative over the derivative and call it the acceleration.

在图上的任意一点,你可以进行求导,得到曲线上每一点的切线斜率,所得到的数值,即为该点处的瞬时速度,然后你再求一次导,得出它的加速度

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