那机械功怎么样呢？

How about mechanical work?

我们是不是也要吃掉，我们做的所有机械功呢？

Don't we have to eat also for all the mechanical work that we do?

热机是指把热能转变为机械功的一种发动机。

By heat engine people mean an engine converting heat energy into mechanical work.

你我一天所做的功，少得令人尴尬，就机械功来说，你可以完全忽略。

The kind of work that you and I do in one day is so embarrassingly little in terms of mechanical work that you can completely neglect it.