Ball Drag

Football 3D Ball Drag
The drag coefficient of a ball plotted against Reynold’s number – a non-dimensional parameter that takes into account both the velocity and diameter of the ball. The drag coefficient drops suddenly when the airflow at the surface of the sphere changes from laminar to turbulent.

The position of the discontinuity depends on the roughness of the surface of the ball. Footballs are relatively smooth and so need to be kicked relatively hard to gain enough speed to move into the turbulent phase.First published in Physics World magazine, June 1998 pp25–27.