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First Law Of Thermodynamics - Intro

The First Law of Thermodynamics is an expression of the principle of conservation of energy. The law states that the change in the internal energy of a closed system is equal to the amount of heat energy added to the system, minus the work done by the system on its surroundings. The total energy of a system can be subdivided and classified in various ways.

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Video Transcript

welcome to the next unit in physics, one of three in this unit. We're going to begin to introduce the laws of thermodynamics by talking about the first law will also be in order to talk about this. We're also going to be defining the terms heat and we're going to be talking about the work done by gas is when they're in these cyclical processes that we've talked about, or even just a single process. And then we're also going to talk about how these are related to energy. If you recall, we've already seen something about work and energy where we said that the total work is done on an object is equal to a change in kinetic energy. And then we were able to expand this out and say that work done by non conservative forces but to a change in potential energy and a change in kinetic energy. And this is what we used to talk about conservation of mechanical energy. If you recall mechanical energy here was equal to you plus K. And we said that this was the total amount of energy involved with the motion of the system. Except sometimes we lose this For example, when we have a non conservative force like friction, it causes a change in kinetic energy that's permanently lost. But where does that energy go? Because the generic concept of conservation of energy is still true. What's happening is that it's being turned into thermal energy and this thermal energy, the heat that you feel when you rub two things together. If we account for it, will actually allow us to continue to ride out a total conservation of energy equation. So that's what we're going for here is to make conservation of energy broader by incorporating thermal energy into our calculations. And when we do that, we'll be able to track Mawr of what's happening to the energias. It changes from kinetic to potential to possibly thermal energy. Um, before we can begin talking about this, what we One thing we need to talk about is what's known as the zeroth law of thermodynamics. And what the zero flaw says is that if we have two objects A and B that air in thermal equilibrium, that means they have the same temperature and that they're no longer passing thermal energy back and forth between each other. If we have those two objects and then we have a second set of objects, B and C, where B is the same object we had before then. That means that A and C must also be at the same temperature and thus in thermal equilibrium. Okay, so what it's saying, then, is that thermal equilibrium is the condition that the two objects are at the same temperature means they're no longer handing back and forth thermal energy. And if we have a set of objects and be there at the same temperature and instead of objects BNC that at the same temperature, then A and C must also be it the temperature at the same temperature. They must be in thermal equilibrium, even if they aren't necessarily touching each other. So this may seem simple, but it's fundamental to the things that we're about to talk about is that even though two things aren't touching each other, they can still be in thermal equilibrium.