Here there's an expansion going on, so the system is doing work to the external world.

这里发生了膨胀,所以系统对外界做功，活塞被推出来。

麻省理工公开课 - 热力学与动力学课程节选

The child has no understanding in any real way of the external world.

儿童对于外部世界并没有什么真正的认识

耶鲁公开课 - 心理学导论课程节选

It's the pressure the external world is applying on this poor system here.

V是气体初态和,末态的体积之差。

麻省理工公开课 - 热力学与动力学课程节选