 Hi everyone. I'm going to talk a little bit about lubricated bearings. Lubricated bearings provide a reduction in friction for rotating members, generally, you know, rotating shafts or things like that within other components. And when we talk about lubricated bearings, usually we're talking about things that are useful for high speed operation, high speed but low load carrying, because instead of having physical things to carry like a force, we're relying on the oil that's used for lubrication. So I have a little drawing on here just as an example. If we have a rotating shaft and it's got a bearing support between the shaft and something that's fixed. And, you know, in this case we might be talking about a thrust bearing which can take on both axial loads as well as radial loads on that part. So when we talk about this rotation, generally we have some sort of lubrication surface between these points of contact, so where there's a rotating object and the non-rotating object, and the amount of lubrication and friction that we see is kind of dependent on a bunch of other factors and whether we're achieving hydrodynamic lubrication or not. So giving kind of an exaggerated view of this, if we had a shaft, so this is my smaller inner circle is the shaft and the outer circle is the hole that the shaft rides in, under no rotation or when it's at rest, we might expect it to look something like this, right? The shaft is going to be sitting on the bottom surface of that hole and, you know, not achieving any form of lubrication, it's just resting there, right? Under slow rotation, again our outer surface and I suppose we have this again, the shaft, this is going to be harder to draw accurately. It's rotating around its center and it's kind of starting to, let's say, climb that inner wall of the hole that it rides in and it's starting to achieve some separation. It's pulling oil through rotation down into that interface between the two things until eventually we get faster rotation in which case we have a film of oil in between those two. So in between the shaft and the hole, we have oil, right? And that of course, you know, means that there's much less friction happening and it requires that the shaft is rotating fast enough that it's pulling oil with it down into that interface and causing it to lift. So really what's happening is as it's rotating we have surface tension and it's pulling the oil with it, building up pressure until that pressure is enough to actually cause the shaft to float on top of the oil. So once it's got high enough pressure built up, then it can lift the shaft and support it on that now pressurized oil and oppose whatever, you know, whatever downward loads in this case might be on the shaft. So, you know, there's a few things affecting this and whether or not we achieve this, you know, hydrodynamic lubrication where we have oil between the rotating shaft and the hole. And there's kind of several things that we would want to consider. The viscosity of the oil, the rotational speed, and then how much load is being placed on that shaft. So, you know, of course, as you might expect, if there's higher viscosity, then we don't need as high of a rotational speed in order to pull the oil because there's going to be greater friction. But of course, greater friction could also be problematic as well, right? If we have higher friction than we really need, then that's inefficiency. We're losing power transmission through that. If we have a higher rotational speed, of course, that means we're going to achieve achieve float easier, right? It lowers our viscosity requirement. So the higher we expect the shaft to rotate, the lower the viscosity of our oil is necessary. But of course, it also, higher rotation also means greater friction, right? So we kind of have a balance there between oil viscosity and rotational velocity. And then of course, the load that's actually applied, so in this case, I'm primarily talking about radial loads, the higher the load, the faster rotation or the higher viscosity oil we need in order to achieve this floating condition. And so we can specify all those things, right? If we know our rotational speed of our shaft, we can use that along with the expected loads in order to design through specification of our oil, right, our oil viscosity. So, you know, we could say an SAE 40 oil versus an SAE 30 oil, where, you know, that that specification is basically how viscous the oil is at measured at 212 degrees Fahrenheit. Similarly, an SAE 10 W versus an SAE 5 W, which is measured at zero degrees Fahrenheit. And we can specify those things depending on on what it is we're trying to do. So that's the general principle of what we're talking about with lubricated bearings. And then I'll be getting into how we actually analyze these bearings in a later video. All right, thanks.