At least two principles work together to produce lift.  Neither completely explains how airplanes fly by themselves.

Bernoulli's Principle

• When air moves faster over an object than under an object, there is less air pressure over the object than under the object. 

• The FORCE of the larger pressure under the object overcomes the FORCE of the smaller pressure on top of the object and pushes the object up.

• Why it does not completely explain flight:

  • The top of a wing would have to be 50% longer than the bottom to generate enough lift for an airplane to stay in the air.  On a typical airplane, the top is only 2-5% longer.

  • Airplanes can do acrobatics - FLY UPSIDE DOWN!  If Bernoulli's Principle explained flight, flying upside down would not be possible.

Newton's Third Law

• For every action, there is an equal and opposite reaction.

  • A wing in flight acts like a scoop and pushes air DOWN.

  • Because of Newton's Third Law, air also pushes the wing UP.

• Note: This explanation implies that the top of the wing is unimportant to flight.  This is NOT TRUE.  How a wing generates lift involves a combination of Bernoulli's Principle AND Newton's Third Law.  Think of them working together on a wing to produce lift.