The principle that explains why airplanes are able to fly is known as the Bernoulli principle. This principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure. Airplane wings are designed to create differences in air pressure above and below the wing, resulting in lift. As air flows faster over the curved upper surface compared to the flatter lower surface, it creates lower pressure above the wing. This pressure difference generates lift, allowing the airplane to rise and maintain flight.