You can actually take derivatives of a vector with time.
你可以直接求位矢对时间的导数
More position vectors? I want to look at that.
例如其它的位矢,我想来看一下
That's the analog of the position vector.
那是和位矢相似的情况
When you vary time a little bit and ask, "How does R change?"
当你把时间改变一个微元,然后问,"位矢 R 会怎样变化"
At every instant, it's got a location given by the vector R; R itself is contained in a pair of numbers, x and y, and they vary with time.
在每一个瞬时,它的位置由位矢 R 给出,R 本身包含了一对坐标值 x 和 y,并且它们都随着时间的变化而变化
We've got one vector which is R.
我们已有的一个矢量,位矢 R
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