Wing aerodynamics. Artwork showing how the wings of an aircraft & a bird generate lift by using the Bernoulli principle. Each wing is shown as a cross section, revealing that it has an aerofoil shape, where the upper surface is more greatly curved than the lower one. The air (blue lines) flowing over the wing has to travel a greater distance in the same amount of time as the air flowing beneath it. Bernoulli's principle states that the faster a gas travels, the lower its internal pressure. The pressure exerted downwards on the wing by the air above it (red arrow) is less than that exerted upwards from below it (green arrow). This difference lifts the wing upwards.