Which term describes the forward force produced by propulsion systems that accelerates air rearward?

• A. Drag
• B. Lift
• C. Thrust
• D. Weight

Answer: (C)

The forward propulsion force produced by propulsion systems that accelerates air rearward is thrust. This is the reaction force created when the engine pushes air backward; by Newton’s third law, the aircraft is pushed forward. The thrust vector acts along the aircraft’s longitudinal axis in the direction of flight, providing the forward push that accelerates and sustains motion. Propellers achieve this by spinning and accelerating air backward, while jet engines do it by expelling exhaust rearward, both producing forward thrust.

For contrast, drag is the backward resistance from air opposing motion, lift is the upward force generated by the wings to support weight, and weight is the downward pull of gravity. Thrust can change with engine power, air density, and speed, but its role remains to propel the aircraft forward.