Common objects can be pure or impure; it just depends whether or not they've been in contact with a source of impurity or not. Alright?

普通的事物可以是纯洁的或者不纯洁的;,原因只取决于它们是否,和一些不纯洁的来源有接触，对吧？

耶鲁公开课 - 旧约导论课程节选

It expands. You change your constraints on your system, you heat it up some more, then you take the heat source away, and you put it back in contact with the atmosphere. And you cool it a little bit, change the constraints, cool it a little bit more, and heat, and you've got a closed cycle engine.

让它与大气接触冷却,改变约束，使它继续冷却，然后又再次加热,这就是循环热机，我们以前也研究过，更复杂的机器。

麻省理工公开课 - 热力学与动力学课程节选