The Boeing 747, like other airplanes, lifts off the ground primarily due to the principles of aerodynamics, specifically the shape of its wings and the thrust produced by its engines.
As the airplane accelerates down the runway, air flows over and under the wings. The wings of a 747 are designed with an airfoil shape, which means they are curved on the top and flatter on the bottom. This shape causes the air pressure to be lower on top of the wing than on the bottom, generating lift. This lift must overcome the weight of the aircraft for it to take off.
Additionally, the engines of the 747 provide the necessary thrust. They work by drawing in air, compressing it, mixing it with fuel, and igniting the mixture. The resulting exhaust gases are expelled at high speed, pushing the airplane forward. As speed increases, more air flows over the wings, increasing lift until it exceeds the gravitational pull on the aircraft. Once the lift is sufficiently strong, the airplane becomes airborne.