What is the definition of the coefficient of drag (Cd)?

The coefficient of drag (Cd) is defined as a dimensionless number that characterizes the drag force experienced by an object in a fluid environment, such as air. This number is fundamentally dependent on the rocket's configuration, including its shape and surface characteristics. When analyzing the aerodynamics of a rocket, Cd is crucial because it quantifies how much aerodynamic resistance the rocket will encounter as it travels through the atmosphere.

A lower Cd indicates that the rocket experiences less drag for a given shape and flow condition, thereby improving performance and efficiency during flight. Factors influencing the coefficient of drag include the angle of attack, surface roughness, and the Reynolds number, all of which are tied to the rocket's design.

In contrast, the other answer choices focus on different aspects of rocketry, such as weight, thrust-to-weight ratio, or stability, which do not specify the concept of drag that Cd encompasses. Understanding Cd is essential for optimizing rocket design and performance.