Final answer:
Viscous drag is the resistance force created by air viscosity within the boundary layer affecting moving objects. Its relationship with object speed can vary from being directly proportional to proportional to the speed squared, while Stoke's law is applied for slow-moving small spheres in viscous fluids.
Step-by-step explanation:
The viscosity of air in the boundary layer creates a drag force known as viscous drag. This drag force is dependent on the object's speed and the characteristics of the flow. For laminar flow, which is smooth and orderly, viscous drag is proportional to the object's speed. However, as the speed or Reynolds number (N'R) increases, the drag force often becomes proportional to the square of the speed, which is a more complex relationship. For example, in bicycle racing, even a slight headwind can cause a significant increase in drag, which impacts the strategy of cyclists. Furthermore, Stoke's law provides a special case where for small spheres moving slowly through a viscous fluid, the drag force (Fs) is proportional to the fluid's viscosity (η), the sphere's radius (R), and its velocity (u), expressed by Fs = 6πRηu.