 Similarly, we can look at acceleration in two dimensions. In one dimension, our acceleration was either a horizontal acceleration or a vertical acceleration, but we just used the A vector symbol. It was a vector because it mattered which direction it was accelerating in, the positive direction or the negative direction. The dimensions were of type length per time squared, and the standard metric unit was meters per second squared. All this part still says the same. We've got the same dimensions and units, but now our vector has both x and y components. If we think again sort of in polar coordinates, A is now the magnitude of the vector, the hypotenuse of that triangle, and theta is still what I use for my direction. Well, in my full standard vector notation, that means that my acceleration vector is a combination of the ax in the i-hat direction plus the ay in the j-hat direction. I still find the magnitude of the acceleration using my Pythagorean theorem, and it's ax squared plus ay squared square root of that whole thing. And if I want to find my direction theta, that's the inverse cosine of the ay over the ax components. And as always, this theta equation is working if you're measuring it relative to the positive x-axis. Graphically, if our vector a is often some direction theta here, then I've got my two components, ax and ay. That shows us a notation we're going to be using for acceleration in two dimensions.