[Sven7]

Originally Posted by ChazInMT

Ha, been sayin this for over a year.

My next step in the logic is after a car passes, we want the air to end up back exactly where it started and remaining stationary. (assuming a calm day)

If we can leave the air how we found it, in my mind it means the air gives back the energy it took to move it up and out of the way in the front part of the shape, so carefully crafting the rear is really essentially, an energy return system.

If the air gets pushed, or dragged forward, or made to spin, this would mean energy from the car had to be put into the air to get it to do so. This is a constant process, much like a fan needs the motor to keep moving a volume of air, the air moving to and fro around a car after it's passage thus represents the drag.

This sort of breaks it down into its simplest form how drag works and why the ideal shape is effective. Straying from the shape invariably means that either by pressure or skin drag, we have caused the air to move more than the ideal shape does and is thus less efficient.

This is so good I'm putting it in my sig. Thanks!