To that end, she says the United States will work with other nations to protect freedom of expression and fight against discrimination and negative stereotyping.

VOA: standard.2009.09.14

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

That's the work that the system is doing to the environment. I'm doing work to the environment. The work is negative, which means that work is being done to the environment.

功的大小,就是矩形的面积,这样我们就实现了一台热机，冷却，加热，加热,冷却，系统回到了初态。

麻省理工公开课 - 热力学与动力学课程节选

Yes. The point is, it's not going to work, and she caught both of them, impressive, it's not going to work because iters left is already negative, it's just going to skip the whole loop, and I'm in trouble, so thank you for catching that.

是的，重点是，程序不会运行的，她发现了两个错误，很令人敬佩，程序不会运行,因为iters，left已经是负数了，它会跳过整个循环，然后就有麻烦了，谢谢你提出这个问题。

麻省理工公开课 - 计算机科学及编程导论课程节选

Delta v is positive in this direction here, the work is negative. So work on the system is positive. Work done by the system is negative.

功是负的，总而言之,外界对系统做功的符号为正。

麻省理工公开课 - 热力学与动力学课程节选

So if delta v is negative, in this case delta v is negative, OK, delta v is negative, pressure is a positive number, negative times negative is positive, work is greater than zero.

也就是当活塞,压缩气体的时候，做的功是正的，按照这一规定,我们需要在这里，加上一个负号，这是习惯规定。

麻省理工公开课 - 热力学与动力学课程节选

This piston is being brought out, so we expect 0 the work to be negative, negative. And we start o V2 ut with zero volume. We end up with a volume p2 of V2, and the external pressure is constant to p2.

所以我们可以想象功是负的,开始的时候体积是,最终的容积是,外界的压力恒为。

麻省理工公开课 - 热力学与动力学课程节选

W2 If I go backwards, to work p1 becomes the negative from what I had p2 calculated before, so this becomes minus what I calculated before for w2.

应该是,总功等于,减去,等于。

麻省理工公开课 - 热力学与动力学课程节选

We could, write the work that we generate -w that comes out as negative w.

的热机相连,热机运行做功。

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