If you tried the paper activity from the front of this article, you might have been surprised by what happened. In most cases a person would think the paper would go down and not lift up when blowing across the top.
It may not be what you would expect, but it is what birds and planes do to lift off the ground and fly. Blowing faster moving air above the sheet paper lowered the air pressure above the paper. Now the air pressure below the paper is higher and creates lift. Lift does exactly what it sounds like, it lifts objects off the ground when everything is just right.
How do you make air move faster?
With the sheet of paper we blew air over the top to create the lower pressure. You cannot do that for birds and planes. Instead the wing of both birds and planes are shaped so that air passing over the top has to travel a longer distance and so it has to speed up as it goes over the top of the wing. This creates the difference in pressure above and below the wing.
How do you get the air to move over a wing?
Getting the air to move over and under the wing also requires the wing to
be moving. This is called thrust. Thrust is created when birds flap their
wings using their strong breast muscles. Planes use another method for
thrust. They use engines. These can be either propeller or jet engines. With
both birds and planes, thrust is the other part of creating lift and the
ability to fly. So the shape of the wing and the ability to move it through
the air are the two things needed for bird and plane flight.
