Bernoulli's Principle states that fluid pressure is reduced whenever the speed of flow is increased. The difference in pressure between two flows is described as dynamic lift. The most common application of Bernoulli's Principle is to the shape of an asymmetrical airplane wing. A curved upper surface produces a faster flow of air than does a lower flat or concave surface, resulting in a pressure differential. Lift of this nature acts on the body in a direction perpendicular to the path of the object movement through a fluid.