Okay, I've told you in the past that metals plastically deform through the sliding of close packed planes like this. And I also hesitated though, and I said there's actually one additional level of complication to it, or not complication, but there's a different mechanism. This is not exactly how plastically, that metals plastically deform. So let's take a look at that now. And and what I want to do is I want to consider a single crystal of a material. So I've drawn a little rectangular solid there and what we're going to try to do is we're going to try to cleave this thing in in half. And so let me illustrate what I mean by that. We're going to apply a force. Okay, we're going to apply a force to this. Here and here. And then what we want to do and we apply the forces is observe it certain deform like this. Okay, and so if we did that, you can imagine that we would, we could we could calculate the the theoretical requirement for that force. If we knew the area and we knew as well what was going on at the interface here. So what I want to do is do a little, want to use a little call out here. And say let's consider that interface. All right, and I told you it's a single crystal. So a single crystal is going to have, you know, some highly organized lattice of atoms. Don't get too hung up on exactly how they're organized here at this point. You know, this type of thing I'm talking about. I want you to draw them all in necessarily, but there's some kind of a lattice of atoms to help make that a little bit more clear. I would draw in sort of the nearest neighbor or the bonds between atoms, if you will, and we'll explore this in more detail later. But what's important is what I'm just trying in there. There's some bonds that span across that area, that cross section. So if we knew the area and we knew the bond density, that is how many atoms, you know, per unit area, and you could work that out from some knowledge of crystal structure. And the bond strength, you could calculate the theoretical value for the strength required to deform the crystal, right? It sounds pretty good. If this was our model, we could do that. And decades ago, that was actually performed. And the problem is that the theoretical strength, that was calculated theoretical. Technically, this is a shear strength, but anyway, the theoretical strength was way over its about, no, corrections, about five times what the actual strength was, five times more than experimental. Okay, so you can do, and experiment, do actually do perform this test and, you know, validate your model, because this is a model of just how metal is plastically deformed. And it's off by five times. So clearly, there's something wrong with this understanding, this model of deformation. So this is actually inaccurate. There's something else. There's a different mechanism going on. And that's what I'd like to show you now. So what I sketched over here with this crystal structure is, is not entirely the whole story. So what we actually often observe a huge quantity of in crystals is this. So it gets in and out to sort of fall along. But right now, you don't necessarily see exactly what I'm trying to illustrate. So if I sketch in the nearest neighbor atoms here, that is the, you know, the direction that the atom rebonded to one another, you'll start to see where this imperfection is. Okay, so this is, it's a certain type of imperfection, but it's a crystalline imperfection. And I like to use the word imperfection rather than defect, although you will hear defect use as well, because defect sometimes has a negative connotation to it. And these imperfections, many of them that will explore, are often used to achieve the properties that we want. They're hugely important in every application of engineering. So these imperfections always exist, but now here's the beauty of it. Watch this. So this is our crystalline imperfection. And what we're trying to, it's a certain type of explain what type later. It's called a dislocation, but we'll explore that later. What we're doing is we're applying a force now, like I said. And what these imperfections allow us to do is this, if you watch that, see, I just break that one bond right there. Okay, and then that bond reforms. Well, now where's the imperfection? Now, which one of these things is not like the other, right? There's, which one, well, this one seems to be missing the rule of atoms, whereas, you know, a moment ago, it was this one. Okay, so, I break one bond and in one fact, this is coming out of the page and into the page. So it's a really a row of bonds. Like I break another one through the application of this force, and then it reforms, and now where's the same perfection? It's moved over again, right? It's moved over step by step. So the end result is actually still the same that this plane of atoms has moved to the right. This one has moved to the left as we illustrated up here. That is to say, you know, this start and end position is correct, but they don't all move together like this. There's actually these imperfections that allow just one row of bonds to break at a time and reform. You know, again, if I can kind of animate this a little bit in a very basic way, I just undo in here and you're going back and forth. So there's what we started with, a bond breaks, another bond breaks and reforms, and it's that step by step movement of bonds that is the mechanism for plastic deformation. So it's a step by step breaking and reforming of bonds, and reforming of bonds. That is the correct mechanism for plastic deformation in the metal. And now that we understand that, the beauty of this, right? It's only good if you can apply it. Now that we understand this, well, there's so many things we could do. What if I went and I put a carbon atom into the lattice like that? And it's going to interact with that movement. Is it going to make it harder? It's going to make it easier. Well, in terms of it's going to make it harder. It could make it stronger. That's the mechanism for alloying. And so what we'll do in the next few videos is explore different types of imperfections. And a lot of times we're going to tie it back to how it interacts with this crystalline imperfection that is the basis for plastic deformation. Because I think plastic deformation right now is an easier property to wrap our heads around. We'll get into some electrical properties later on. But mechanical is a good one to wrap our heads around to introduce these imperfections. Okay? Thanks a lot.