How Does an Airplane Stay in the Air?

Airplane flight relies on four forces: lift (upward), weight (downward), thrust (forward from engines), and drag (backward from air resistance). Lift is generated primarily by the wing shape (aerofoil) and its angle of attack. As the wing moves through the air, it deflects airflow downward; by Newton third law, the air exerts an equal and opposite force upward on the wing. Additionally, the curved upper surface causes air to accelerate, lowering pressure above the wing relative to below (described by Bernoulli principle). Both effects contribute to lift. An airplane takes off when lift exceeds weight, and cruises when all four forces are in equilibrium.