So, it's the second derivative of a position vector.

它是位置向量的二阶导。

youdao

And this, now, is the position vector of the center of mass.

现在，这里是，物体的矢量中心。

youdao

And this, now, is the position vector of the center of mass.

现在，这里是，物体的矢量中心。

youdao