This particle is constantly changing its direction, but it therefore has an acceleration and the acceleration, we have shown here, is pointing towards the center.

这个质点恒定地改变它的运动方向,因此它具有加速度,而且这个加速度,我们前面也讲过了,指向圆心

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The tangent's pointing towards the direction you are headed at that instant.

切线的方向就是,速度矢量在那个瞬时的指向

耶鲁公开课 - 基础物理课程节选

That means the acceleration is pointing towards the center of the circle and it has a magnitude a.

也就是说加速度,始终指向圆心,其模长为 a

耶鲁公开课 - 基础物理课程节选