Science and Math For Technology

Pressure drag accounts for much of the drag as objects move through the air or water. Molecules of air or water build up near the frontal area of an object. This increases the pressure on the frontal area of the object, which slows movement through the air or water. Pressure drag on a baseball is more than 90% of the total drag because of its shape. Because pressure drag depends on the shape of the body, it is sometimes referred to as profile drag.

The side of an automobile drawn on a piece of paper would be the profile drag for that vehicle. The bumpers and windshield would account for much of the drag. Increasing the width or height of the automobile increases the drag.

As drag pressure increases in the front of an object, air pressure decreases behind the object. An example would be the effect of a motorcycle traveling along a race track. The air behind the motorcycle forms a low pressure area. A practice called drafting takes place when a second motorcycle follows directly behind the lead motorcycle. The air molecules do not come back together again until they pass by the second motorcycle. This second motorcycle has less frontal pressure drag and uses less energy to travel at the same speed as the lead motorcycle.