 So, I'd like to talk now about a concept of how to apply the ideal gas law to the workings of a jet engine in pretty basics, okay? Pretty basic. So, what I'm going to do here is I'm going to write four words and when I write these four words, one of two things is going to happen. You're either going to kind of chuckle or giggle a little bit like my high school students often do and you're probably also going to wonder what in the world do these words have to do with the ideal gas law and a jet engine. So let me write these words here. All right. Where do those words come from? What in the world are you writing? All right. Well, I asked a friend who actually worked for a place that manufactures jet engines. What types of things would you want students to know or think or understand about the work you do if I was teaching a class in aerospace engineering? And he said, here's four words that they should learn because that'll help them remember the workings, the basic ideas, the workings of a jet engine. And those words were, and I raised my eyebrow a little bit too when he said this, suck, squeeze, bang, blow. Well, let's see how those apply to the ideal gas law and to the workings of a jet engine. First of all, let's recall the ideal gas law. And I'm going to use the, well, normally it's PV equals nRT. But I'm going to rewrite it this way as a ratio. PV over nT is equal to some constant, where our values are our pressure, our volume, our amount of gas, and our temperature, OK? So how does that work? How do we apply the ideal gas law to the jet engine? Well, here's what we're going to try to do here. At the end of the jet engine, one of the things we want to do is we recognize that there's a pressure outside, a P naught, OK? There's a pressure outside here. And that if the jet engine's not turned on and not moving, there's also a pressure inside, which is the same as the pressure outside, OK? But what we'd like to do, that same pressure outside is also the pressure out here. But if we can get a change in the pressure where the pressure inside is much greater than the pressure outside, that's going to push a bunch of stuff out of the back, and it's going to create thrust. And we'll talk about thrust more later in another video or later in the class. Well, that's the blow part. We'll get to there. If we can change, get a big difference in pressure where there's more pressure here than there's pressure outside, we'll blow everything out the back, and that will create thrust, and that's how a jet engine works. So how do we create that difference in pressure? And here's where the ideal gas law comes in. We start off by recognizing, OK, in order to make this work, we're going to bring in a whole bunch of air. We're going to suck in a whole bunch of air from outside. And as we suck in that air, we're adding to that system. There we go. We're adding in a whole bunch of air. We're going to add to that system a bunch of mass into the system. OK? Well, recognizing that p over n, there's v and t as well, pv over nt, but what we're going to do is we're going to say we're adding a bunch of stuff, thought a closed system. We're adding a bunch of stuff to the system. And when we add stuff to the system, assuming the other things stay the same, they don't quite. There's some variations in there. But that's going to tend to make my pressure go up. We're adding a bunch of stuff and putting it into this system. The more stuff we add, pressure has a tendency to build. That's the suck part. Then we squeeze. We use a change in geometry. We use some baffles to sort of push things in, and we take all that air and we squeeze it down into a smaller and smaller space. There's a squeeze part. Well, when we're squeezing, again, looking at pv over nt, squeezing makes the volume go down. Well, if the volume goes down, assuming the other two say somewhat the same, what's that going to tend to do to the pressure? It's going to make the pressure go up. Notice we're not assuming the temperature is probably not heating up very much there. And we're not adding more stuff. We already added more stuff over here, whereas over here, the volume was pretty much sustained until we started shrinking it. So in two ways, we've made the pressure go up, first by bringing stuff in and then squeezing that stuff down. Then step three, bang, what do we do here? We take it and we light it on fire. Well, wait a minute. You can't add air on fire, but what we do is we add fuel. We add some rocket fuel, something that can explode, something that can burn. And when we do that, two things happen. Let me rewrite pv over nt again. First of all, we are adding jet fuel. That is, once again, adding more mass. We're adding it to the system. But in addition to adding it to the system, we set it on fire, which releases a whole bunch of energy and heats up everything in the system, which raises the temperature. It gets nice and hot in there. Nice and toasty. Well, both of those things, as part of the bang, lead to a major increase in pressure. So we've increased it by adding stuff. We've increased it by shrinking stuff. We've increased it by adding more stuff and exploding it, heating it up. And now we have a pressure inside that's a lot greater than the pressure outside, and we just let her go. We let it blow out the back. And that's how we create thrust using the principles of the ideal gas law.