What effect does drag have on an aircraft's movement?

Drag is a force that opposes an aircraft's motion through the air. When an aircraft is in flight, it generates lift which allows it to rise, but drag acts in the opposite direction to the aircraft’s forward motion. As a result, drag directly affects the aircraft's speed by reducing the forward thrust provided by the engines.

When drag increases, it necessitates that the engines work harder to maintain speed or altitude, which can lead to a decrease in overall performance and efficiency. If the force of drag exceeds the thrust produced by the engines, the aircraft will decelerate or slow down. This means that managing drag is essential for maintaining optimal flight conditions and ensuring safe operation, particularly during phases like takeoff, climb, and descent.

In contrast, the other options do not accurately describe the fundamental effect of drag on aircraft movement. While lift is important for maintaining altitude, drag does not increase it. Instead, drag counteracts any attempts to accelerate, and to claim that it has no significant impact would negate its foundational role in aerodynamics and aircraft control.