Which option best describes thrust?

• A. The force opposing forward motion
• B. The force produced by wings generating lift
• C. The force produced by the engine that pushes air backward to create forward motion
• D. The resisting force that slows descent

Answer: (C)

Thrust is the forward-acting force created by the propulsion system. It comes from the engine driving a propeller or a jet, which accelerates air backward. Newton’s third law tells us that pushing air backward produces an opposite reaction on the airplane, pushing it forward. This is the mechanism that generates forward motion and propels the aircraft.

This is different from drag, which is the resistance that opposes forward motion; lift, which is the upward force produced mainly by the wings to support weight; and weight, the downward pull of gravity. In steady, level flight, thrust balances drag, while lift and weight determine altitude and airspeed. So identifying thrust as the force produced by the engine that pushes air backward to create forward motion best captures both how it’s generated and what it does.