The physics of a putted ball; the USGA and R&A agree on COR; how loft works

Golf Digest, July, 2002 by Frank Thomas

What happens to a golf ball immediately after impact with a putter? There are two opinions in our office. One school of thought is that the ball never breaks contact with the putting surface; the other insists the ball does leave the ground, even if it's for just a nanosecond.

John DiMiceli, Somers, N.Y.

Most putters have some degree of loft--3 degrees is average. For a 10-foot putt, if the putterhead is traveling horizontally at the time of impact, the ball will be struck slightly below its equator. As the illustration below shows, this does two things: First, it lifts the ball off the surface of the green ever so slightly. Second, it creates a small amount of backspin.

When the ball lands back on the ground (about two or three inches after it has left the putterface), it will start skidding. This sliding motion will stop the backspin and produce forward or rolling spin. Pure rolling will be achieved about 15 inches from where the ball was first struck. If a putter has no loft and the putting motion is the same as above, the ball will start by skidding or sliding before it achieves pure rolling spin.

Hope you were on the right side of the argument.

I've read that the U.S. Golf Association and Royal & Ancient Golf Club of St. Andrews have come to an agreement on regulating the springlike effect on drivers. How will this proposal affect us weekend golfers, and how will it affect tour players?

Dennis White, Buffalo, N.Y.

If the proposal is adopted (this is not a sure thing yet), it would mean that starting next year you could play a driver with a higher coefficient of restitution (COR) than the USGA now permits (.860 versus .830). If you play one of the newly "street-legal" drivers, you may gain a few yards when you hit the ball on the sweet spot. Unfortunately, most of us don't hit it that pure very often.

The May 9 proposal would affect tour pros who use nonconforming drivers in events played outside the United States and Mexico. As of Jan. 1, 2003, they would have to use drivers that conform with the USGA's .830 limit.

So soon you (not the tour pros) may be able to go up to .860. But it's not forever: The proposed agreement would allow you to tee up that hot driver only until 2008, when the COR limit on all drivers drops to .830.

I have noticed that some companies' irons have higher lofts than others. For example, some have pitching wedges with 48 degrees of loft, while other PWs have 45 degrees. Does this difference in loft affect the distance you get with the club?

Dustin Redger, Newton, Kan.

Loft does affect the distance you hit the ball. For example, the difference in loft between a 5-iron and a 6-iron is about 4 degrees. The shaft length between clubs also changes by about a half-inch. If both clubs are struck well, the difference in distance will be about 15 yards. Therefore, you can expect about half this from a change of 3 degrees in loft for a wedge, if the lengths are the same.

The golf equipment industry once had an unwritten standard for lofts, but when some manufacturers tried to convince golfers that their clubs were longer than other brands--simply by reducing the loft on, say, the 5-iron--the unwritten standard flew out the window.

Frank Thomas, technical
director of the USGA from
1974-2000, is Golf Digest's
Chief Technical Advisor.
E-mail him at equipment

@golfdigest.com.