来自《耶鲁大学开放课程：基础物理 第1集 第1集》
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like sines and cosines.比如正弦函数和余弦函数 -
So if you don't know that then,如果你还不知道这些 -
of course,you have to work harder than other people.那你当然要比别人花更多功夫了 -
If you know that, that may be enough for quite some time.如果你都知道 那在很长一段时间里都足够了 -
So what I've said so far is,到目前为止 我说过 -
a particle moving in time from point to point一个质点随时间的连续运动 -
can be represented by a graph, x versus t.可以用一幅x-t图来表示 -
At any point on the graph在图上的任意一点 -
you can take the derivative,你可以进行求导 -
which will be tangent to the curve at each point,得到曲线上每一点的切线斜率 -
and its numerical value will be所得到的数值 -
what you can call the instantaneous velocity of that point即为该点处的瞬时速度