How does a bird's wing lift a body into the air?

A bird's wing stays up by pushing air downward. A wing is an airfoil, a shape built so that the air gives it a net upward force while the air itself is sent down. Newton's third law does the rest: if the wing shoves air down, the air shoves the wing up with an equal and opposite force. That upward push is lift.

Here is the catch. The explanation most of us met at school says air must race over the curved top of the wing to catch up with air going underneath, because both have to arrive at the same moment, and faster air means lower pressure. It is a tidy story, and it is incorrect. Physicists point out that no difference in path length is needed, and the air over a lifting wing in fact moves much faster than that story predicts. The speed-up is real, and Bernoulli's principle is fine. What fails is the idea that a longer path explains the speed.

The fuller picture is a partnership. Flowing past the wing, the air ends up at lower pressure above it and higher pressure below it, so the underside pushes up harder than the top pushes down. Physicists stress that speed and pressure influence each other, rather than one simply causing the other.

Tilt matters too. Raise the wing's angle to the wind and it deflects more air and lifts more, up to a limit. Go past it and the air peels away from the top of the wing, the lift drops, and the wing stalls.

A bird adds one thing that a glider lacks: flapping. The wings keep making lift, and the flight muscles tilt that force forward so it also acts as thrust.