首先，对左手边的系统做功。

First of all, work is being done to the system on the left-hand side.

youdao

这里发生了膨胀,所以系统对外界做功，活塞被推出来。

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

youdao

好的，首先,我们通过左边对系统做功。

OK, so w, first of all, work is being done to the system on the left hand side here.

youdao

Somebody say it real loud. Yes, the system is working on the surroundings, right? It's pushing out against them.

有人很大声的回答了，对，系统在对外做功，他把外界向外推开。

麻省理工公开课 - 热力学与动力学课程节选

Thermodynamics is asking you, what work does this thing do on the surroundings or the surroundings do on the system?

热力学在问你们，到底是系统对环境做功,还是环境对系统做功？

麻省理工公开课 - 热力学与动力学课程节选

No, we call that work positive work. All right, so that means we need to put a negative sign right here, by convention.

历史上有过不同的习惯，这里我们规定,如果环境对系统做功。

麻省理工公开课 - 热力学与动力学课程节选