Aerodynamic Drag in Automobiles

Aerodynamic Drag is the force that opposes an automobile’s motion through the air. Drag is created in the direction of the moving air when the air pressure encounters a solid object. Drag is generally undesirable because power is required to overcome it.

To quantify the amount of drag on an automobile, we use a value called the drag coefficient (cd). This number depends on the shape of the automobile , its speed and surface roughness, the density of the air and the nature of the air flow (laminar (smooth) or turbulent).

Forces that influence drag include the air pressure against the automobile, the amount of friction along the sides of the automobile’s body and the relatively negative pressure, or suction, on behind the automobile.