 So let's start off with a little bit of a review of positions in physics. And to define position, we're talking about a location relative to some reference point, or more precisely, where is an object at. Because it's a physical quantity we're measuring, we're going to have dimensions and units, and for these particular things, it's dimensions of length, and the standard metric unit we're going to be using is meters. Now the simplest type of positions we can talk about are positions along a line, or what we call 1D. So if I've got some sort of line, I'm going to describe where I am along this line. When I've got a horizontal line, I typically use the variable x to describe that position. So I might be describing a car as being 3 meters to the right of a particular reference point. So my x is going to be equal to 3 meters there. Now know that I can be either on the right or the left side. So the right side were these positive positions for x, and the left side is going to be the negative positions. So position has not just a value associated with it, but also which direction am I? Now most problems aren't limited to just a line. So we open it up then for two dimensions. And so this is where we've got our x, y grid. And I can describe my position in x but also my position in y by using those set of x, y coordinates. So I could be over 2 meters in x and up 3 meters in y, and that's going to give me my position relative to some reference point here. x and y isn't the only way I can describe positions though because I also have that polar coordinates. And in that case I've got not a square grid but the circular coordinate system where r tells me how far out I am from the origin. And then theta tells me where am I at going around the origin. So I can use either x, y or r, theta to describe my position in 2D. Now again, our general physics that we're starting with in these classes, we're going to work with the simpler problems that can be described pretty easily along a line or maybe on a flat plane. But to fully describe reality in physics, we have to use 3 dimensions and that gives us our position in space. So it's not just x and y, but we're actually going to have an x, a y and a z. So in our simple problems we might start off with 1 dimension, move up to 2 dimensions, but always recognize that that 3rd dimension is there and we'll briefly look at how to handle those things as well. Again, this is just a brief overview of positions in physics that are going to kind of set up some of the rest of our discussion here.