So expansion work, for instance, or compression work, is if you have a piston with a gas in it. All right, you put a pressure on this piston here, and you compress the gas down. This is compression work.

力乘以距离，就是功，功有许多种：,电可以做功,驱动电机与电风扇,磁力也可以做功。

麻省理工公开课 - 热力学与动力学课程节选