Areas of Aerodynamics
Race Cars
Speed boats
The car in the picture above shows how the car acts as a wing. Vacuum at the rear of the car will take the weight off of the rear tires. This brings in the need for spoilers or other devices to keep the tires in contact with the ground. Some examples of these are:
The spoiler creates a force downward to counter act the vacuum created by the square back.
Another way to get downward force is to use scoops. The way it works is that air goes into the box and expands, creating another downward force that will keep the car on the ground
Pictures courtesy of Matt Gartner (c) 1999