Newton's third law of motion comes into play through interaction of these forces. That law states that for every action there is an equal and opposite reaction. An aircraft is in level steady flight when the upward force of lift equals the downward force of gravity caused by the aircraft's weight and when the backward force of drag and is counterbalanced by the forward force of thrust. The mass of an object that equals the downward force of gravity pulling it to Earth.
Gravity pulls the aircraft to Earth in a force equal to the weight of the aircraft.
The upward force that raises an airfoil when fast-moving air passes over the top of the shape. Lift is the force that reacts against the weight. It is created when air moves over the airfoil shape of the wing, causing a decrease in air pressure on top of the wing and a reaction, or push upwards from the greater pressure beneath the wing. The forward force countering drag is thrust. Thrust may be provided by an engine turning a propeller that pushes air backwards as it spins or by a jet engine ejecting hot gas backward.