Aerodynamics
When air flows over a race car body, it does two things: It causes drag, and it causes downward pressure, usually called down force. Drag is an enemy, and down force is a friend, but the two are completely related. You cannot have down force without drag. Air also plays an important role inside certain parts of the car. For example, the engine and brakes need air for cooling, or they will melt.

When a race car moves down the track, the biggest thing by far slowing it down is the air. The car has to push the air around and over the body. The faster the car goes, the more air it has to push out of the way. The energy it takes to push all of this air out of the way is called drag. You can actually feel the drag when you stick your hand out the car window on the freeway. You feel the wind pushing your hand back. In reality, your hand is pushing lots of air out of the way.

Photo courtesy Action Sports Photography, Inc.

The interesting thing about drag is that it is not linear. When the speed of a car doubles, the drag on the car does not double. It actually goes up by a factor or four. Even with their super-powerful engines, there is so much drag at 200 MPH that the engines have to run at full power just to push all the air out of the way!

NASCAR designers use air to their advantage. By giving a NASCAR race car a certain shape, it helps the air create down force on the car. A typical NASCAR race car body creates about 1,500 pounds of down force. In other words, as the air moves over the car, it pushes down on the car with a force of about 1,500 pounds. That's a big help in the turns because it keeps the car on the ground and helps the tires stick better to the track.

Photo courtesy Action Sports Photography, Inc.

Drivers also use air to their advantage, by driving closely behind - within inches of - the car directly in front. By getting behind someone else, you let the car in front do a lot of that air-pushing work. Your engine does not have to work as hard, which saves you gas and pit stops.

But there's an interesting side effect to drafting. If you pull in behind a car to cut your own wind resistance, you actually help the car in front go faster too. Two cars running together can go 6 to 7 MPH faster than a single car running alone. That's because a car running alone creates a vacuum behind it, and that vacuum causes a lot of drag. When a car pulls in behind another car, it fills that vacuum. Now the car in front has less drag, and can go faster.