 Now we examine uniform circular motion. In uniform circular motion, part of our definition is that the object moves in a circular path. Now mathematically, that means that our radius is constant. So if I place my coordinate of my origin in my coordinate system there at the center, then every place along that path has the same value for r. And we use just a regular r to represent that radius. The object also has to move at constant speed. So as it's moving around this circle, the actual speed it moves with doesn't change. And it could be moving counterclockwise or clockwise around the circle. Doesn't matter. You can still have uniform circular motion if it moves at constant speed. Now in terms of our equations again, that speed is the magnitude of the velocity. So we're going to use just the regular v to represent our speed now. Now if I want to find out what that speed is, it goes once around that circle in a set time period. So if I measure some places my starting place, I want to go once around. And that's going to be the circumference of the circle in however much time it takes to go once around. So I can measure the speed then as 2 pi r, the circumference of the circle, divided by the time it takes to go once around. And this time period, the time it takes to go once around, is called just the plane period. So they shortened down time period for once around the circle to just period. And you can calculate the period then by using 2 pi r over the velocity. So if you're given the speed and the radius, you can find the period. If you're given the radius and the period, you can find the speed. Now before we move on, we want to note that even though the speed is not changing, the velocity does change because the direction of motion is changing. I think about my circle again. As I move around the circle over here on this edge, I might be moving upwards, where now I'm moving to the left. By the time I get to this side of the circle, I'm moving downwards. And when I move over here to this side of the circle, I'm now moving to the right. So the direction of motion changes, even if I stay going counterclockwise the entire time. So that direction or the velocity change, that velocity vector is changing. And so that means there does have to be in an acceleration. So uniform circular motion has a constant radius, a constant speed, but the velocity is changing. And so there is an acceleration. That's a brief introduction to uniform circular motion. We'll take a look at a couple of very closely related concepts here soon.