What is the definition of drag?

The definition of drag specifically refers to a natural force that acts against the forward movement of an aircraft, effectively slowing it down in flight. This force arises primarily due to the interaction between the aircraft's surfaces and the air through which it moves, as well as the shape and design of the aircraft itself.

In aerodynamics, drag is typically classified into several types, including parasitic drag and induced drag, but the core concept remains that it opposes the thrust produced by engines, thereby reducing the overall efficiency of the aircraft's movement. Understanding drag is crucial for pilots and engineers alike, as it influences fuel consumption, flight speed, and altitude performance.

The other options describe different concepts related to flight dynamics but do not capture the essence of drag. For instance, a force that assists in acceleration is more accurately attributed to thrust. Aerodynamic lift is an essential force that allows an aircraft to rise and stay airborne, while the weight added for stability pertains to different aspects of aircraft design and control, rather than the resistance force known as drag.