ON THE EDGE

The Forsyth-Barr effect

Tue, 18 Sep 2012 16:30
Dunedin-stadium630

There could be a scientific explanation for the poor goal-kicking at Dunedin's enclosed Stadium.

The Forsyth-Barr Stadium has been a tough venue for goal-kickers ever since it was first used at the World Cup last year, which has been something of a conundrum considering the fact that it has a roof.

Springbok flyhalf Morne Steyn was the latest player to battle off the tee, when he missed a number of seemingly straight forward kicks in the Springboks' defeat on Saturday, and scientist Brian Wilkens believes he has an explanation.

Wilkens told Fairfax Media that the issue relates to the lateral Magnus/Robins force, which makes any spun ball curve when the air flowing around it leaves the surface earlier on one side than on the other.

"In rugby, most kickers don't strike the ball dead centre and their boot doesn't come through straight in line with the target; they come around the ball slightly," Wilkins said.

"They're almost guaranteed to put a slight sideways spin on the ball. It's the same sort of thing as table tennis, when you put side spin on the ball it swerves.

"It's the smooth non-turbulent air [under the roof] which accentuates all these phenomena. It's only got to be a very slight rotation for it to take off and develop into a big curve," he added.
 

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