Have you ever wondered what makes a kite fly, or what a kite and an airplane have in common? The truth is that they both rely on the same science―the science of flight. Basics of Flight There are four main forces involved in flight: lift, weight, thrust, and drag. Lift is created by the difference in air pressure between the air flowing over an airplane's wings and the air flowing under them. Lift is opposed by weight, which is the force of gravity that is constantly pulling the airplane down. If the amount of lift is greater than the amount of weight, the airplane will rise. At the same time, thrust is created by the airplane's engines and propellers pushing the airplane forward. Opposed to that force is drag, which is the air pushing the airplane back. If thrust is greater than drag, the airplane will move forward. The interaction between these four forces makes airplanes fly.