"It took the modern science of fluid dynamics to understand exactly what happens in a swerving free kick", says Dr Ken Bray in BBC News. "Above a certain speed - about 12 mph for a football - a miraculous thing happens. Turbulence begins to move backwards, producing a boundary layer - a layer of very thin flow very close to the ball's surface - and this has the effect of causing the air flow to cling more closely to the ball's surface." Later he says:
"When the ball rotates the boundary layer remains tripped but the air flow separation around the ball is distorted. Separation occurs earlier on the side rotating against the flow and later on the side rotating in the same sense as the flow. This causes a pressure differential and a deflecting force which is responsible for moving the ball in the air in a free kick."
It will be interesting to watch the new World Cup ball, Adidas' 'Teamgeist', fly and curve, especially in penalty shoots!
Baseball, anyone?
