Lift is a commonly used term to describe "something" that results in objects moving upwards against the force caused by gravity. This "something" is actually a force in itself. Lift is one of the four main forces that act upon all objects that move through the air. These four forces are:
# Lift - an upward force on the object
# Weight - a downward force due to the acceleration of gravity
# Thrust - a forward force (propulsion)
# Drag - a force caused by resistance that acts in the opposite direction of thrust
Lift is a simple concept to grasp, yet the reason it exists is a complex one. To this day there is still great debate over what is the cause of lift. There are several popular explanations given which are commonly found in student textbooks, and even pilot training manuals, yet these popular explanations do not stand up to serious physics analysis. The most common of these arguments is based off of Bernoulli’s Principle.
As it has been named, "Bernoulli’s" argument states that the reason lift is created in wings is that the upper surface of the wing is curved, and therefore longer than the underside of the wing (In truth, Bernoulli had nothing to do with this explanation of lift, it is only attributed to his principle). The argument goes on to say that if the upper surface is longer than that of the bottom, the air flowing over the upper surface must travel faster as it has farther to travel. Using Bernoulli’s Principle this explanation says that because the air traveling over the top of the wing is moving faster than the air under the wing the air above the wing exerts less pressure on the wing than the air under the wing. If there is less pressure above the wing then the air under the wing will push upwards on the wing, generating lift.
This explanation is flawed on several accounts, yet many people still believe it. It is rather appealing because it is simple and makes some logical sense. In addition, it is not completely wrong either. Although it makes a few assumptions incorrectly, Bernoulli’s Principle still applies to certain wings under specific conditions. What this explanation does not take into account is how planes are able to fly upside down, or how symmetrical wings (such as stunt plane wings that are the same length on top and bottom) create lift, or even how children's toy planes with flat wings create lift. This explanation of lift is also dependent upon what is known as "the equal transit time" concept. This concept states that air that is parted as it hits a wing must meet back up at the end of the wing. This is incorrect. In truth the air above the wing actually moves much faster then the air below so that it is a ways beyond the same section of air underneath the wing once both have passed.
This model and experiment ideas are provided by The National Aeronautics and Space Administration and The Glenn Research Center.
So now the question is, what causes lift?
The Newtonian Approach (Flow Turning)