Because it's so important. And I should add and also under reversible work, where the external pressure is equal to the internal pressure.

而且我还要说应该在外部压强,和内部压强相等的,可逆过程中引入它。

麻省理工公开课 - 热力学与动力学课程节选

p We want p equal to p external for the entire expansion, p2 and p external is decreased steadily from p1 to p2.

在膨胀过程中保持p等于外部，外部p很快从p1衰减到。

麻省理工公开课 - 热力学与动力学课程节选

But it shouldn't depend on extrinsic, external facts about what's happening someplace else.

但不该依赖于外部，在别处发生什么等等外在事实。

耶鲁公开课 - 死亡课程节选

It becomes,in part,an external affair.

在某种程度上，它变成了外部事件。

耶鲁公开课 - 死亡课程节选