方向：面相切接触，并与物体的相对运动趋势的方向相反。

Direction: physiognomy tangential contact with, and objects with relative movement trends in opposite directions.

youdao

But things which were at rest will move at a constant velocity, opposite of the velocity that you have relative to me.

这些静止的东西都在匀速运动,方向正好跟你相对我运动的速度方向相反

耶鲁公开课 - 基础物理课程节选