So, normally at this point, we do actually start class with a little bit of history from alchemy to modern chemistry, but I decided to skip that this year.

通常在这个时候,我们要从一些从炼金术,到现代化学的历史出发正式开始我们的课程。

麻省理工公开课 - 化学原理课程节选

it's clear that you want to add a vector that looks like that, because then you go from the start of this to the finish of that, you end up at the same point and you get this invisible 0 vector.

显然应该给它加上这样一个矢量,因为从这个矢量的起点指向那个矢量的终点,最终指向的是同一个点,你就得到这个不可见的零矢量

耶鲁公开课 - 基础物理课程节选