So if we want to talk about the volume of that, we just talk about the surface area, which is 4 pi r squared, and we multiply that by the thickness d r.

如果我们要讨论它的体积，我们要用的是表面面积，也就是４πｒ的平方，乘以厚度ｄｒ

麻省理工公开课 - 化学原理课程节选

r And what that is the probability of finding an electron in some shell where we define the thickness as d r, some distance, r, from the nucleus.

在某个位置为,厚度为dr的壳层内,找到原子,的概率，我们来考虑下我们这里所说的。

麻省理工公开课 - 化学原理课程节选

The most important result from last time was that if you took this r, and you took two derivatives of this to find the acceleration, d^2 r over dt^2, try to do this in your head.

上节课最重要的结论,就是如果你把 r 写成这样,对 r 求两次导就能得到加速度,d^2 r / dt^2,心算一下

耶鲁公开课 - 基础物理课程节选