How can something so big and so heavy fly. Several forces act on an airplane. A force is a push or a pull on something. You use force when you throw a ball, pull a wagon, or walk. When you walk, you push backward on the floor, and the resistance from the floor pushes you forward.
Forces always work in pairs, on different bodies, in opposite directions, and at the same time.
Four main forces act on airplanes. Lift acts upward and allows the airplane to fly. The weight of the airplane acts downward. Thrust is the force that moves the airplane forward. The force that holds an airplane back is called drag .