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.

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。

youdao

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.

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。

youdao

So now we're going to turn off the lights and I want to show you the motion of the center of mass.

我们要关上灯，我想给你们展示，质量重心的运动。

youdao