Drag force is the resistance an object experiences when moving through a fluid, such as air or water. This force acts opposite to the direction of the object's motion and increases with the object's speed. Factors influencing drag force include the object's shape, size, and the fluid's density and viscosity. In the context of aerodynamics, drag force is crucial for understanding how vehicles like cars and airplanes perform. Engineers design these vehicles to minimize drag, improving fuel efficiency and speed. The study of drag force is essential in fields like sports science and marine engineering, where optimizing performance is key.