Bernoulli's Principle

Bernoulli's principle is regarded by many as a paradox because currents and winds upset things, but standing a stick in a stream of water helps to clarify the enigma. You will see calm, smooth, level water ahead of the stick and a cavity of reduced pressure behind it. Calm water pushes the stick, as lower pressure downstream fails to balance the upsetting force.

Bernoulli's principle never acts alone; it also comes with molecular entrainment. Molecules in the lower pressure of faster flow aspirate and whisk away molecules from the higher pressure of slower flow. Solid obstacles such as airfoils carry a very thin stagnant layer of air with them. A swift low-pressure airstream takes some molecules from this boundary layer and reduces molecular impacts on that surface of the wing across which the airstream moves faster.

For Bernoulli's principle to dominate a dynamic situation, friction must be less dominant. Elastic molecular impacts are frictionless—no heating. Molecules of dry air, even more than those of water, collide elastically; so Bernoulli's principle with its molecular-entrainment agent is dominate for windy air.