now I'm really fantastic at drawing this mechanical device, but you can imagine that dropping a weight can cause a paddle wheel to turn.

机械装置的时候,我真的很着迷，你可以想象,当重物掉落的时候会带动桨轮旋转。

麻省理工公开课 - 热力学与动力学课程节选

When we have just a single bond in them molecule, you have all the free rotation you want, you can just spin it around, there's nothing keeping it in place.

当我们在分子力只有一个单键时，你可以随意旋转，你可以让它转起来，没有什么东西能固定住它。

麻省理工公开课 - 化学原理课程节选