What are the four forces acting on an aircraft in flight?

The correct answer identifies the four fundamental forces acting on an aircraft during flight: lift, weight, thrust, and drag.

Lift is the upward force generated by the wings of the aircraft as they move through the air. This force is critical for overcoming gravity (weight), which pulls the aircraft downward. Thrust is the forward force produced by the aircraft's engines, allowing it to move ahead. Finally, drag is the resistance force that acts opposite to the direction of flight, caused by aerodynamic friction as the aircraft travels through the air.

Understanding these four forces is essential for analyzing how an aircraft behaves in flight. Each force plays a significant role in the aircraft's performance, stability, and ability to maneuver. For example, achieving sustained flight requires lift to be greater than or equal to weight, while successful navigation through the air also relies on managing thrust against drag.

In contrast, the other choices do not encapsulate all four essential forces correctly. Instead, they introduce concepts or forces that are not primary forces impacting flight dynamics, such as momentum or pressure, which are not classified as the fundamental forces acting on an aircraft.