Which force opposes the forward motion of an aircraft?

The force that opposes the forward motion of an aircraft is drag. Drag is a resistive force that acts against the direction of an aircraft’s thrust, slowing it down as it moves through the air. This force originates primarily from the friction between the aircraft's surface and the air, as well as from the pressure differences that occur as the aircraft moves at speed.

In contrast, thrust is the force that propels the aircraft forward, created by engines. Lift counters the weight of the aircraft by allowing it to rise into the air, and weight is the force due to gravity that pulls the aircraft down towards the Earth. Understanding the role of drag is crucial for pilots, engineers, and anyone involved in aviation, as it significantly affects the aircraft's performance, fuel efficiency, and overall flight dynamics.