 We're going to take a look at the coolest free body diagram you're ever going to get to make for an inclined plane. We'll start off just by drawing a triangle, like a ramp. We'll put a box or some sort of object on top of that triangle. Now what are the forces that act on the box? Well, there's a force of gravity acting straight down on the box. There's also a normal force, and we're used to drawing the normal force going straight up when the object's on a horizontal surface, but normal actually means right angle. So we have to make the normal force at a right angle to the surface. There's also this other strange force that kind of pulls the box down the ramp. We're going to look at that in a moment. Now how do we figure out the value of that normal force if it's not exactly the same as gravity just in the opposite direction? Well, I can actually take that normal force vector, and I can slide it down a little bit so it is next to the force of gravity. You can also take that weird other little force vector and put it down there as well. And when I do that, what I end up with is our triangle, a right angle triangle. And the neat thing about this is the angle of incline that's in the ramp is exactly the same as the top angle in that right angle triangle. Now if we do a little bit of trigonometry here, we can see that the hypotenuse of the right angle triangle is the force of gravity. We can calculate that just using force of gravity equals mg. And we can calculate the adjacent side, which is the normal force, by taking the cosine of the angle of incline and multiplying that by the force of gravity. I can also find the opposite side of the triangle, which is called the parallel force. We call it that because it's the force of gravity parallel to the incline. And I can find that by taking the side of the angle of incline and multiplying by the force of gravity. And now that we know all of the three sides of that triangle, we can go and solve all sorts of free body diagram force problems for incline planes.