We know that birds stay in the air due to lift, an upward force produced by the difference in air pressure above and below the wings. This air-pressure difference is, in turn, the result of air...

We know that birds stay in the air due to lift, an upward force produced by the difference in air pressure above and below the wings. This air-pressure difference is, in turn, the result of air flowing more quickly over the top of the wing than below the wing. Let’s experiment with airflow and air pressure using a tissue. Hold the tissue vertically and blow on one side of it—the side you blow on is analogous to the top of the wing, where air flows faster. What happens to the tissue? Does it do what you expect? Can you produce enough lift to keep the tissue horizontal?