The Wind Tunnel (Page 5)

There's another interesting aspect of the Reynolds number. For given shapes particular Reynolds numbers reflect a laminar flow or turbulent flow. Really high numbers generally mean that a flow is turbulent. If you think of smoke coming off of a candle, first there is a nice smooth (laminar) stream of smoke and then the smoke swirls and twirls around (turbulence).

Rough surfaces and shapes that are not streamlined tend to cause turbulence because the air can not flow smoothly across a surface. That's why airplane wing surfaces are smooth and shaped the way they are. The air can gracefully negotiate a smooth turn across the wings surface. A brick, with its blunt shape, is not a very aerodynamic shape.

In the case of the tennis ball - the fuzz tends to create turbulence. And in our videos we demonstrate how a smooth and rough surface ball change the aerodynamics of the flow.