One way to think about it, if we want to use a classical analogy, which often helps to give us an idea of what's going on, is the spin of an electron, we can picture it rotating on its own axis.

如果我们用一个，经典的比喻来考虑它的话，这经常会帮助我们建立起一些概念，就是我们可以把电子的，自旋想象是它绕着轴自转。

麻省理工公开课 - 化学原理课程节选

The other thing that's on this slide here is sort of a simple analogy that I've already described.

这张幻灯片上的其它东西,是一个简单的类比,我已经讲过了

耶鲁公开课 - 生物医学工程探索课程节选