There are two theories of how lift occurs on a wing. Both are correct and both are useful in explaining the forces on an airplane.
The conventional and classic Longer Path explanation uses the Bernoulli effect. The top surface of the wing is more curved than the bottom side. Air traveling over the top of the wing has a greater distance to go—a longer path—than air passing underneath the wing. So the air over the top of the wing must travel faster than the air under the wing. The air passing over the top of the wing and from below the wing must meet behind the wing, otherwise a vacuum would be left in space. The Bernoulli principle states that faster-moving airflow develops less pressure, while the slower-moving air has more pressure. That greater pressure on the bottom of the wing is termed “lift.” Basically, this pressure difference creates an upward suction on the top of the wing.
The competing but complementary theory is based on Isaac Newton’s third law of motion, the law of action and reaction, which states that “for every action there is an equal and opposite reaction. When air molecules hit the bottom surface of the wing at a glancing angle, they bounce off and are pushed downward. The opposite reaction is the wing’s being pushed upward. Hence, we have lift. It’s similar to BBs hitting a metal plate—they’ll rebound backward. BBs go in one direction and the metal plate goes in the opposite direction.
As it turns out, the Bernoulli Longer Path theory is a better explanation of lift for slower-speed planes, including jet airliners. Newton’s third law is best suited for hypersonic planes that fly high in the thin air at more than five times the speed of sound.
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There are two theories of how lift occurs on a wing. Both are correct and both are useful in explaining the forces on an airplane.
The conventional and classic Longer Path explanation uses the Bernoulli effect. The top surface of the wing is more curved than the bottom side. Air traveling over the top of the wing has a greater distance to go—a longer path—than air passing underneath the wing. So the air over the top of the wing must travel faster than the air under the wing. The air passing over the top of the wing and from below the wing must meet behind the wing, otherwise a vacuum would be left in space. The Bernoulli principle states that faster-moving airflow develops less pressure, while the slower-moving air has more pressure. That greater pressure on the bottom of the wing is termed “lift.” Basically, this pressure difference creates an upward suction on the top of the wing.
The competing but complementary theory is based on Isaac Newton’s third law of motion, the law of action and reaction, which states that “for every action there is an equal and opposite reaction. When air molecules hit the bottom surface of the wing at a glancing angle, they bounce off and are pushed downward. The opposite reaction is the wing’s being pushed upward. Hence, we have lift. It’s similar to BBs hitting a metal plate—they’ll rebound backward. BBs go in one direction and the metal plate goes in the opposite direction.
As it turns out, the Bernoulli Longer Path theory is a better explanation of lift for slower-speed planes, including jet airliners. Newton’s third law is best suited for hypersonic planes that fly high in the thin air at more than five times the speed of sound.