What is induced drag?

Induced drag is a type of aerodynamic drag that arises specifically due to the generation of lift. When an aircraft's wing creates lift, it also affects the airflow around the wing, leading to the formation of vortexes at the tips. These vortexes increase the drag acting on the wing, which is referred to as induced drag. As lift increases, induced drag also increases, which is why this type of drag is particularly relevant during conditions where the aircraft is generating significant lift, such as during takeoff and climbing.

The other options focus on different aspects of drag, such as surface roughness, which relates to skin friction drag, not induced drag. A vacuum doesn't allow for airflow or lift generation, making it irrelevant to the concept of drag in an aerodynamic context. Lastly, while weight does influence various flight characteristics, it doesn’t directly cause induced drag; rather, it's the lift generation that leads to this specific drag type.