Well, we're going to part four of lecture four of bluff body aerodynamics. So for cars, the most useful way of thinking about the drag is breaking it down by components. The third of the three techniques that were introduced to the lower earlier. So here's the components. We're going to be thinking about its form drag, induced drag, cooling air drag, roughness drag, and interference drag. We'll revisit these more in the next lecture in a couple of weeks and more detail. For now, let's think a little bit about form and induced drag. I can't really separate these from one another to be honest. They're basically the drag sources that come just from the shape of the vehicle itself. Because this inevitably leads to the generation of streamwinds, vortices, there's some induced drag that also occurs. And that's related to lift generation as well. But again, it's very difficult to separate out these two things. So this considers sort of the basic vehicle shape. So we've got no wheels, no cooling air flow, nothing like door handles, no side mirrors. The underbody is sort of made to be smooth, the wheel houses are filled in. So basically this is kind of like a flying object near the ground. This is what we mean by the basic form. And this basic shape has a pretty low drag coefficient. It turns out, so here's some shapes for reference. So we've got sort of this ellipse-soight, which has a CD-0.06. I have a 2D version of that ellipse-soight, it's 0.14. It's sort of car, hatchback type shape is only a little worse, 0.17. And it's better than a sphere, for example. And much better than sort of just a cylinder with a blunt trailing edge. Now if we change the inclination of the body relative to the floor, this is going to alter both the lift and the drag. For a car, we can alter that inclination by the design of the suspension. We can make the front or rear of the car slightly higher than the other end. So because we have the ability to do this, it makes sense to determine what orientation is going to minimize the drag. There's a bit of terminology here that inclination relative to the road is what we'll call an angle's attack. So at a positive angle attack, the front end of the vehicle will be higher than the other end. So for our kind of basic form flying car shape, the minimum drag tends to occur at a negative lift. We can see that here on this plot, at sort of a negative lift coefficient of a point, negative 0.13, we get this the minimum drag coefficient. And at a zero lift, we have sort of a drag coefficient that's somewhat higher. But realistic vehicle shapes with the wheels and everything added actually produce positive lift at the minimum drag condition. And this is not really ideal because it reduces the downforce on the wheels and reduces the handling capability of the car. The wheels and the vortices associated with the account for this main difference, and this is one of the reasons why we sometimes need to put features on vehicles to try to add down force even though it comes with the expensive additional drag.