That limit will be some arrow we can call the velocity at the time and it will always be tangent to the curve.

那个极限也就是一个矢量,我们称之为瞬时速度,并且它总是和轨迹相切的

耶鲁公开课 - 基础物理课程节选

p2 p1 is greater than p2. Then I want to reverse direction of time. I want the arrow of time to go so that the gas goes from p2 to p1.

一直推，一直推，p1大于,接下来我想让时间倒流,让气体从p2到p1。p2比p1小。

麻省理工公开课 - 热力学与动力学课程节选

So, for the most part any time we talk about or draw pointers an arrow suffices, which really 71 in there is a number like 71, which is the literal byte that the F is actually in in RAM, but frankly who cares?

所以，每次我们讨论,或者用箭头表示指针,在指针里面有一个数字，如,那是F在RAM中的字节，但是谁在乎它呢？

哈佛公开课 - 计算机科学课程节选