What is the force called that opposes thrust during flight?

The force that opposes thrust during flight is known as drag. Drag is a resistive force that occurs due to the motion of the aircraft through the air, and it acts in the opposite direction of the flight path. As an aircraft moves forward, it displaces air particles, which creates a pressure difference and results in drag. This aerodynamic force counteracts the forward motion generated by thrust from the engines or propellers.

Understanding drag is crucial for aircraft design and performance because it directly affects fuel efficiency and the overall operation of the aircraft. Pilots and engineers must consider drag to optimize speed, control, and fuel consumption, especially during takeoff, cruising, and landing phases.

While weight, lift, and gravity are all essential forces acting on an aircraft, they do not specifically oppose thrust. Weight pulls the aircraft down due to gravity, lift acts upwards to counteract weight, and gravity itself is the force that attracts the aircraft toward the Earth. In the context of opposing thrust during flight, drag is the most relevant force to focus on.