So here's how well off you are, here is time, and you start with nothing and you end up incredibly well off.

纵坐标代表你的处境，横坐标代表时间，你从一无所有到辉煌腾达。

耶鲁公开课 - 死亡课程节选

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