When swinging at a golf ball, the objective is to strike the ball in the center of the club head commonly known as the "sweet spot". Inevitably, golf balls will be struck off center and an interesting physics situation occurs.

A perfectly hit ball creates an enormous amount of backspin, approximately 3500 rpm. To achieve this, the ball while it is in contact with the club for 0.5 ms must obtain a pure rolling motion. What happens if the ball is not hit in the center?

If the ball were hit off center and the ball is rolling on the club face we might expect it to spin in the opposite direction, clockwise in figure 1. This is not the case, since the club puts a large force on the ball, by Newton's third law, the ball puts a large force on the club ~17500 N. This force rotates the club head in the direction of "F x r". Therefore the ball in this brief impact rolls producing a spin in the opposite direction.

If the club face were flat, every golf shot hit off center would not find it's way into the fairway, but since it is convex the path will initially travel in a direction normal to the club face and curve back into the fairway.

Penner⁵ finds that the optimum radius of curvature of a club face for a 200g driver should be 21.5 cm. Increasing the mass would increase the curvature.