How do airplanes generate lift?

Airplanes fly because their wings generate lift, a force that pushes them upward. As a wing moves through the air, its shape and slight upward tilt deflect the oncoming air downward; by Newtons third law, the air pushes the wing upward in reaction. At the same time, air moving over the curved upper surface travels in a way that produces lower pressure above the wing than below it, and this pressure difference also lifts the wing. Both explanations describe the same physical reality. Lift increases with speed and with the angle of the wing, which is why aircraft must reach a high speed on the runway before they can take off.