Then again, you will find the evolution of the planetary motion, because the rate of change of the rate of the change of the position is connected to the position.

同样地,这就是行星运动的演化过程,因为行星位移的变化率的变化率,与它的位移有关

耶鲁公开课 - 基础物理课程节选

For example, if you started here and you did all this and you came back here, the average velocity would be zero, because you start and end at the same value of x, you get something; 0 divided by time will still be 0.

例如,如果你从这里开始运动,经过这个过程又回到这里,平均速度就是0,因为初态和末态的位移相同,你得到了什么呢,0除以时间还是0

耶鲁公开课 - 基础物理课程节选