That's the analog of the position vector.

那是和位矢相似的情况

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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

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It's not enough to say these are the components of the vector; you've got to tell me, "I am working with i and j, which I define in the following manner."

所以,只说"这些是某矢量的分量"是不够的,你还得告诉我,"我选取的基矢是 i 和 j,它们是这样定义的"

耶鲁公开课 - 基础物理课程节选