Which four forces act on an aircraft in flight?

The correct response identifies the four fundamental forces acting on an aircraft in flight: lift, gravity, thrust, and drag.

Lift is the upward force generated by the wings as they move through the air, enabling the aircraft to rise. This force counteracts gravity, which pulls the aircraft downward towards the Earth. Thrust is the forward force produced by engines that propels the aircraft through the air, while drag is the resistance that opposes this forward motion, caused mainly by air friction against the aircraft's surface.

Understanding these four forces is crucial for comprehending the principles of flight, as they interact to determine an aircraft's performance during various phases of flight, including takeoff, cruising, and landing. Together, they play a vital role in the dynamics of how an aircraft operates in the air.