Which set correctly lists the four forces acting on an airplane in flight?

• A. Lift, weight, thrust and drag
• B. Lift, weight, gravity and inertia
• C. Thrust, drag, weight and acceleration
• D. Lift, drag, weight and momentum

Answer: (A)

Four forces act on an airplane in flight: lift, weight, thrust, and drag. Lift is the upward force created by the wings as air moves over them, working against weight, which is the gravitational force pulling the aircraft downward. Thrust is the forward push produced by the engine or propeller, while drag is the resistive force acting opposite the direction of motion. In steady, level flight these forces balance (lift equals weight and thrust equals drag), so there’s no net acceleration. Other terms like gravity, inertia, or momentum aren’t separate forces in this context: gravity is what creates weight, inertia is a property of mass, and momentum is a motion quantity, not a force.