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Each molecule has a certain location, certain velocity. ![]() The atoms and molecules that form the liquid or the gas always have well-defined states. At the microscopic level – it’s no secret – we all know everything is made of atoms and molecules. So, you’ve got to understand that temperature and thermal equilibrium represent gross macroscopic properties and they’re not always defined. But if you wait long enough until the two parts have gotten to know each other, they will turn into some undrinkable mess, but the nice thing is it will have a well-defined temperature. Some parts are hot, some parts are cold that system doesn’t have a temperature. For example, if you just poured it from the top, the hot stuff is on the top, the cold stuff is on the bottom, there’s a period of transition when you really cannot even say what the temperature of the mixture is. If you now pour one of these cups into the other one, that’s going to be a period when the system is not in equilibrium in the sense that it doesn’t have a well-defined temperature. They are both in a state of equilibrium.Įquilibrium is when the macroscopic properties of the system have stopped changing. Here’s another cup of cold drink at what we feel is a lower temperature. But I’m talking about a cup of coffee that’s been isolated from everything it maintains the temperature. If you leave a cup of coffee in this room, it will cool down because the room has got a different temperature. So, it will settle down to some temperature and it will maintain the temperature. Now, we have not defined what temperature it is precisely, but we can talk about whether whatever it is has changed or not changed. We say it’s in a state of thermal equilibrium because this temperature does not seem to change. We think they maintain a certain temperature. If you take a cup of hot water, and you take another cup of cold water, each cup, if you waited sufficiently long, is said to be in a state of equilibrium as long as the cups were isolated from the outside world and not allowed to cool down or heat up. So, I’ll tell you what equilibrium is with a concrete example. Just like mechanical equilibrium, this is a very important concept. That introduces the notion of what is called thermodynamic equilibrium. Even that requires a little more precision. So, let’s say you have the notion of hot and cold. But as physicists, of course, we want to be more precise, more careful. So, hang on to that that’s the right intuition. So, we are going to start with the intuitive definition of temperature everybody has. So, the whole next four lectures are devoted to the study of heat, temperature, heat transfer, things like that. And there’s also stuff you probably have seen in high school, some of it at least. Okay, so this is another new topic on thermodynamics, a fresh beginning for those who want a fresh beginning. Then, I will probably give you one last problem set with two or three problems on whatever I do near the end. I’m giving enough time so you can plan your moves. ![]() ![]() I’m going to assign something today which is due next Wednesday. We’re going to have a slightly different schedule for the problem sets. Professor Ramamurti Shankar: Alright class, welcome back. Temperature as a Macroscopic Thermodynamic Property Fundamentals of Physics I PHYS 200 - Lecture 21 - ThermodynamicsĬhapter 1.
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