We didn't have that in the eight-millimeter days. We had to lug a projector, we had to plug it in to somebody's wall, put up a screen and show it to someone patient enough to sit there for five minutes and watch.

VOA: special.2011.06.20

There are many kinds of work. There's electrical work, take the motor, you plug it into the wall, electricity makes the fan go around, that's electrical work. There's magnetic work.

我们复习一下大一,学过的功的概念：,物体在力的作用下，运动了一段距离。

麻省理工公开课 - 热力学与动力学课程节选