Another climber,John Lang, suggested Bachar free-solo an area called Double Cross, in Joshua Tree National Park,California.

VOA: special.2009.12.09

The piston has a cross-sectional area, a, and the force pressure is force per volume area.

我们以活塞系统为例，来说明膨胀功。

麻省理工公开课 - 热力学与动力学课程节选