Which force opposes an airplane's forward motion?

The force that opposes an airplane's forward motion is drag. This force arises primarily from air resistance as the airplane moves through the atmosphere. When an aircraft accelerates, it pushes the air in front of it, creating a turbulent region around itself. As the air flows around the aircraft, it exerts a retarding force on the airplane, known as drag.

Drag is crucial to understand because it directly affects an aircraft's performance; a higher drag force requires more thrust to maintain steady flight at a constant speed. Managing drag is essential for efficient flight operations, which is why engineers design aircraft shapes to minimize it.

Lift, on the other hand, is the upward force that counters weight, allowing the airplane to ascend. Thrust is the forward force produced by engines that propels the aircraft. Weight is the gravitational force pulling the aircraft towards the Earth. While all these forces play roles in flight dynamics, drag specifically acts to slow down the airplane, making it the correct answer to the question regarding which force opposes forward motion.