As in many machines, a big wheel makes the little wheels turn.

VOA: special.2009.11.29

now I'm really fantastic at drawing this mechanical device, but you can imagine that dropping a weight can cause a paddle wheel to turn.

机械装置的时候,我真的很着迷，你可以想象,当重物掉落的时候会带动桨轮旋转。

麻省理工公开课 - 热力学与动力学课程节选

Your steering wheel works, so you can turn the trolley car, if you want to, onto the side track killing the one but sparing the five.

而你的方向盘还没坏，只要你想，就可以把电车转到侧轨上去,牺牲一人挽救五人性命。

耶鲁公开课 - 公正课程节选