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Adiabatic can be either reversible or not, and we're going to do that probably next time or two times.
绝热过程可以是可逆的，也可以不是，我们可能会在下一次或下下次课上,研究这个问题。
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Because it's so important. And I should add and also under reversible work, where the external pressure is equal to the internal pressure.
而且我还要说应该在外部压强,和内部压强相等的,可逆过程中引入它。
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it was reversible, so you can give people money and take it away, and you could actually scale the amount of money, so it makes a very handy experimental tool.
这个过程是可逆的，这样你可以给人钱，然后拿走，而且你还可以积攒钱，这就让钱成为了一种非常有用的试验工具。
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As long as it's reversible, you know what the efficiency has to be, and in principle, you could break it down into a bunch of steps that you could formulate as isothermal and adiabatic.
只要这个循环过程是可逆的，你们知道效率是多少，从理论上说，可以将总过程,分解成一系列绝热,和等温的小过程。
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One is our Carnot engine as we've seen it, and the other is just any other reversible engine.
一个是我们已经学过的卡诺热机，另一个是任何一个其它可逆热机。
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And what you'll find is that the maximum work out is obtain for a reversible path.
对于各种可能的中间路径，我们将发现,做功做多的是可逆路径。
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And all we know about this is that it's really for some irreversible reversible step.
我们知道,这个式子,对不可逆过程成立。
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Let's just take our reversible engine and modify it a little bit.
我们就拿可逆热机为研究对象,并对它进行一点修改。
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we're going to have a difference here between the irreversible case and the reversible one.
可逆过程,和不可逆过程,会有不同。
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I can do that because it's reversible, and I can get a functional form out.
画出路径就意味着过程是可逆的，下面我们来看这条曲线的函数形式。
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And probably also in practice nothing is truly reversible.
或许在实践中,没有什么是真正可逆的。
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If it was non-reversible, I would be allowed to put an initial point and a final point, but I wouldn't be allowed to put a path between them like this, connecting them together.
如果是不可逆过程，我可以画出过程的初态点,和末态点，但是我不能再像这样,画出连接这两个点的，路径曲线来。
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And now since it's reversible, we can run it forward or backward.
因为它是可逆的，所以可以正方向运行。
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Like something is almost reversible and almost irreversible.
就像什么东西是几乎可逆的,或几乎不可逆的。
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And again, I want to stress this is a reversible path.
再强调一次，我们研究的是可逆过程。
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STUDENT: Is there a boundary between reversible and irreversible?
学生：可逆与不可逆间,有没有边界？
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So we're going to start at one, T1 and this is going to be in isotherm at temperature T1, and all the paths here are going to be reversible.
我们从一开始，这是个绝热恒温过程，温度是，所有路径都是可逆的。
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PROFESSOR: A boundary between reversible and irreversible?
教授：可逆与,不可逆间的边界？
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And you know, you could have a reversible engine with lots and lots of steps, but you could always break them down into some sequence of adiabatic and isothermal steps.
你们知道，我们可以设计一个由，很多很多个,循环步骤的热机，但是总可以把它分割成,一系列的绝热,和等温过程。
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But you don't compress it so quickly that you're not in there reversible process so you compress that if you were to feel the temperature of the air and you can feel it through the nozzle gives you an idea of the temperature of the air inside your bicycle pump.
但是压缩速度,也不能太快,否则就不是,可逆过程了,这样当压缩气体时,从喷嘴可以感受到,内部气体的温度。
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TdS It comes from the fact that dq reversible is T dS, pdV and dw reversible is minus p dV.
这个结论来自于：可逆过程下dq等于，做功dw等负的。
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Now q2 was in this step, and we're going to leave that reversible, right, but q1 is irreversible.
现在q2是这个过程中的热，是一个可逆的，但是q1是不可逆的。
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That's equivalent to doing the integral, and so, what we end up getting is that the reversible work v2 pdv is equal to minus integral V1, V2, p dV.
这与刚才的积分过程效果相同，最后，我们得到的结论是可逆过程的功,是负的积分，从v1到。
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