Video narration
How can a heavy aeroplane stay in the sky? It comes down to four forces acting on it all the time: lift, weight, thrust, and drag. Weight pulls the plane down because of gravity. Lift is the upward force made mainly by the wings as air flows around them. As the plane moves forward, the wing meets the air at a slight angle. Air is guided over the top and under the bottom, creating higher pressure underneath and lower pressure above, which pushes the wing upward. That’s lift. To keep moving forward, the engines provide thrust. But the air pushes back with drag, like wind resistance. In steady flight, lift balances weight, and thrust balances drag. Change the speed or the wing angle, and you change lift—so the plane can climb, descend, or stay level.