# Secret of Ball Sports

A main secret of all ball sports is how to make the ball follow a curved path. This is acheived by spinning the ball which creates an unsymmetric separation of the air flow around the ball and thereby creates a lift force curving the path. This is referred to as the Magnus effect.

Vol 4 shows that the magnitude of the Magnus effect and thus the curvature, depends on the position of the separation, which is influenced by the speed and spin of the ball and also on the roughness of the ball surface, and of course on the size and weight of the ball.

Another secret is referred to the so called drag crisis with a drastically reduced drag for Reynolds numbers in the range from 100 000 to 1 million. The reduced drag is related to the delayed separation which may occur if the boundary layer is turbulent (instead of laminar) prior to separation.

Vol 4 simulates the drag crisis in the flow around a sphere using Euler/G2 combined with a skin friction boundary condition.