这紫外线光可以，与小球互动，也就是质量重心，当周围暗下来，能看到质量重心运动。

And ultraviolet light will interact with that little ball, the center of mass, and when I then make it dark, you will only see the motion of the center of mass.

youdao

结果显示：（1）背越式跳高最大的优越性是弧线助跑起跳能经济实效的降低和升高身体重心，为身体重心运动方向的提早转变和垂直速度的提早积累、增大创造有利条件。

The result is :(1) the most superiority of flop is the approach can change the gravity of body, so that accumulate favorable circumstances for the transform timely of body-gravity.

youdao

我向你们提到过,重心的运动是稳定的,若不受外力，我可以再次演示,在空气轨上。

So I mentioned to you that the motion of the center of mass is very uniform in the absence of external forces, and that I can demonstrate for you again with the air track.

youdao