You can make an airfoil using a piece of notebook paper and a book. Place the paper between two pages of the book, leaving one end of paper hanging out. Close the book. When you direct air over the top of the paper, it rises upward, illustrating lift.
Move air over your airfoil by blowing on it or by moving the book quickly through the air. Either way, you see the paper rise. This is due to the shape of the airfoil. This airfoil is simple, but it uses the same principles employed in making airplane wings and propellers.
When air is in motion, some passes over the top of the airfoil, and some passes under the bottom. Because of its shape, as air passes above and below an airfoil, the air at the top speeds up, which decreases the air pressure in that area. The air below maintains a constant speed, and so has a higher pressure. This pressure differential illustrates Bernoulli's principle. As air moves more quickly, there is a greater difference in air pressure. When the differential is high enough, lift is achieved, and the piece of notebook paper ? or the wing of an airplane ? rises into the air.