我们在上节课讲了推力和拉力，可产生加速度。

Last time we discussed that an acceleration is caused by a push or by a pull.

youdao

原本是圆周运动，突然间，推力和拉力都没有了，这就会呈螺旋状运动，显然，这是不对的。

You go around in a circle, and all of a sudden you no longer have the pull or the push and you go around in a spiral and obviously, that is not the case.

youdao

拉力和推力，你都需要。

You need both the pull and the push.

youdao

Then, you may have forces to the right, forces to the left pushing, pulling.

然后你就有向右的力,和向左的力,推力和拉力都有

耶鲁公开课 - 基础物理课程节选