Here there's an expansion going on, so the system is doing work to the external world.

这里发生了膨胀,所以系统对外界做功，活塞被推出来。

麻省理工公开课 - 热力学与动力学课程节选

Convention, OK, this negative sign is just a pure convention. You just got to use it all the time. If you use an old textbook, written when I was taking thermodynamics, they have the opposite convention, and it's very confusing. But now we've all agreed on this convention, and work is going to be with the negative sign here.

系统对外界做功的符号为负,这就是我们,在本课中的规定，纯粹出于统一符号的需要，有些教科书中，可能会使用相反的符号规定,注意不要混淆了，这门课上,我们将一直使用。

麻省理工公开课 - 热力学与动力学课程节选

The first one that I'd like to mention today is Christina Roberto who is a grad student who is working at The Rudd Center who's right here, a teaching fellow for the class, is going to be doing some very interesting work on health policies and people's food intake.

今天我想介绍的第一位是,克里斯蒂娜·罗伯特,她是在路德研究中心工作的研究生,她也是我们班的助教,正坐在下面,她将要从事一些关于,医疗卫生政策和人类食物摄取的有趣工作

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

I also want to assume for our present purposes that there's only pressure volume work going on, which is to say I want to put pdV p dV in here minus p dV for dw.

同时假定,对于我们目前的目的而言，只有压强做功这就是说,我要把这里的dw替换为负。

麻省理工公开课 - 热力学与动力学课程节选