Lift is the force that holds a plane in the air. You might be
wondering, how can a wing float on nothing? Well, air is actually
a physical substance; it's a mixture of several gases (including
oxygen, carbon dioxide, and nitrogen) and it has lots of molecules
moving around. Even though you can't see those molecules, they
have a weight and can exert pressure on a kite or a balloon
or a plane. In order to have the most lift, airplane wings are
shaped so that the air flows faster on top of the wing than
underneath. The faster air moves, the less pressure it has,
so the slower-moving air underneath the wings creates more pressure
and pushes the wing up. In order for a plane to fly, it has
to have enough lift to overcome its weight, also known as gravity.
In 1901, the Wright brothers grew frustrated with the results
of their experiments. The gliders didn't fly as long or as
far as they expected them to. Plus, most of the landings were
crash landings, so the Wright brothers had to bring the glider
back to the shop to fix it before it could be flown again.
Finally, Orville and Wilbur built a small wind tunnel out
of a wooden box and a gas powered fan. They placed model metal
wings inside the wind tunnel and measured how well they lifted
with a scale and balance. This way they were able to find
the best wing shape without crashing real planes!