# Curve on golf club sends ball straight

Golf club makers build a slight bulge into the striking surface of the driver–a club used to smack balls a long way. Now, a scientist has calculated why that bulge helps balls curve to the middle of the fairway rather than hooking or slicing.

The analysis by physicist A. Raymond Penner of Malaspina University-College in Nanaimo, British Columbia, also shows that curvatures typical of commercial driver heads are near to the mathematically determined optimum.

“I was quite surprised that it came out so close,” says Penner, noting that the driver surface was developed by trial and error.

In the October American Journal of Physics, Penner presents the equations and numbers behind a balance of effects already familiar to many students of golf. On one side of that balance is the so-called gear effect. That’s a skewing of the ball’s course by the spin that the club puts on a ball hit off center. The curve results from aerodynamic forces that the spin produces. As a counterbalance, the curvature of the driver directs the ball in the opposite direction and nullifies some of the spin from the gear effect. The result is a ball more likely to end up in the middle of the fairway than it would if hit with a flat club surface.

Manufacturers have missed two other factors, Penner reports. Harder-hitting golfers need more-sharply curved driver heads to keep their drives in line, whereas those using popular, larger-volume driver heads need less curvature, he says.