As I wrote in my previous article, despite the nonsense that you see and read online, or may even get from a teacher in an in-person lesson, you are not missing putts because you are putting spin on the ball. What you are absolutely doing, however, is skidding the ball. In order to understand why the ball skids, and how you can minimize skid and have better control of your putts, we have to take a look at the forces that are acting on the ball when it is struck by the putter, and after.
There are two main forces acting on a putted ball which determine how the ball moves: the impact force which the putter imposes on the ball (which becomes momentum once the ball leaves the club face) and the friction between the ball and the putting surface*. These two forces are opposing; that is, they act in opposite directions—but more importantly, they act at different points on the ball.
Because the contact between the club face and the ball when putting is so close to the equator, or midline, of the ball, the impact force is very closely aligned to the ball’s center of mass (sometimes referred to as the center of gravity, or CG), so the impact force (and after impact, momentum), acts at the center of the ball, while the friction force, as shown in the illustration below, acts at the periphery, or outer surface, of the ball.
 |
| Impact force or momentum, opposed by friction, causes the ball to roll |
The force of impact, and then momentum, translates the ball, while the tangential friction, acting at the periphery of the ball much like a hand on the steering wheel of a car, turns the ball around its center, causing it to roll. If a ball were struck while sitting on a hypothetical frictionless surface, without the opposing force of friction acting at its periphery, the ball would simply slide, translating without rolling, so the friction between the ball and the putting surface is an important factor in the launch conditions of a putt.
 |
If impact force or momentum is not opposed by friction the ball will translate without rolling. |
It is effectively impossible to achieve instantaneous roll at contact except in a very short, very lightly struck putt—a tap-in, or a steep downhill putt. For a putt of any distance (depending, of course, upon the friction characteristics of the putting surface), where the force of the initial impact is greater than the frictional force between the ball and the surface, the ball skids, slipping on the putting surface until the torque imposed by friction increases the spin rate to match the translational speed of the ball. This happens on nearly every putt, to some extent, and to improve your putting performance you have to understand why it happens, and what you can do to minimize it.
The length of the skid phase depends upon several factors: the delivered loft of the putter face (that is, the vertical angle of the club face at impact with the ball: static loft + dynamic loft); how hard the ball is hit; and the amount of friction between the ball and the putting surface and between the club face and the ball.
The illustration below shows a putter with 2˚ of effective loft at the moment of contact with the ball. The angle of the face places the impact point approximately 30 thousandths of an inch below the equator, or horizontal midline, of the ball (that’s about 1/32 of an inch; you know, those divisions on your scale that you can just about make out without putting on your reading glasses? Or maybe that’s just me.) The red arrows in the illustration depict the impact force vector and its horizontal and vertical components.
 |
| The slight positive loft on the putter face tends to lift the ball at impact. |
The vertical component of the impact force, though small, is important. Its presence means that the ball is being nudged upwards slightly by the impact of the club face. There are those who will tell you that this upward nudge is necessary to get the ball out of the slight depression it creates in the putting surface by its own weight (including the folks at Scotty Cameron, who cite in-house studies that they say confirm this. Color me skeptical.)
What that upward nudge will do is off-weight the ball slightly at the beginning of its movement—if not lift it entirely free of the surface momentarily. The effect of this reduction in the contact between the ball and the putting surface is a reduction in the frictional force which induces roll, and therefore an increase in initial skidding.
Because positive loft, even in amounts as small as the standard 3.0˚ to 3.5˚ found on most putters, places the point of impact below the ball’s equator, it also adds a small counter-spin rotational force component to the motion of the ball, which works against the friction-induced force that creates forward rotation. The combination of upward nudge and counter-rotational force contributes to the ball’s tendency to skid, and must be reduced to minimize skid and optimize launch conditions.
I wasn’t able to find any studies which examined skidding with regard to control—that is, staying on line, but it has been shown to be important to achieving consistent distance control.
There was an interesting study** done in 2014 by Jeremy Pope, Paul Wood, and Erik Henrikson, of Ping Golf in Phoenix, Arizona, and David James of Sheffield Hallam University, Sheffield, England, which primarily focused on the effect of skidding distance on distance control. Utilizing putters with loft angles of 5˚, 3˚, 1˚ and –1˚, this study found that the putter with –1˚ loft performed best in terms of minimizing skid distance and producing consistent total putting distance, on both natural and artificial turf surfaces. (Take that, Scotty Cameron.)
I did a quick survey of putter manufacturers as background for this article, and learned (as mentioned above) that the standard loft for off-the-rack putters is around 3.0˚ to 3.5˚, with customization available from some manufacturers of from +3˚ to -2˚ (note that none of these number yield the negative loft which performed best in the 2014 study.)
Setting aside variables like turf type, turf condition, moisture, mow height, etc., one thing that can be stated with certainty is that a too-high delivered loft will increase skid distance, and can even result in a ball that lifts off of the putting surface slightly as it leaves the club face, resulting in a bouncing motion. This is bad for both distance and direction control.
Some studies cited in the book The Science of the Perfect Swing, by Peter Dewhurst—a rather dense little volume that will test your math and physics knowledge, your patience, and your eyesight (8-point type? Really?)—claim results that showed that the skid phase of a putted ball is typically one-seventh of the total distance of the putt, regardless of the length of the putt. Honestly, I find that hard to believe, and I have to wonder at the test conditions and methods that led to such conclusions.
My own home-grown testing, on a firm industrial carpet surface that stimps at about 13 to 14 (at a guess), using my stable of four putters which are all bent to a loft of approximately –1˚, showed mostly pure skid for the first two to four inches from contact, as shown on slow-motion video, with full rolling contact occurring at between six and eight inches on eight-foot putts.
As is always the case in putting there are a number of variables that affect the results, and the friction characteristics of the artificial putting surface I practice on is certainly one of them, but scientific studies and my own on-course experience have convinced me of the effectiveness of a slight negative loft.
(No brag, just fact: At the media preview for the 2019 U.S. Open at Pebble Beach, I managed four one-putt greens and eleven two-putts† in near-U.S. Open conditions with my mongrelized Tight Lies Anser-clone putter, counter-weighted and bent to a –1˚ loft. )
If warranted by on-course conditions, such as a soft, slow putting surface due to mow height or moisture, it is always possible to increase dynamic loft by moving the ball forward in your stance, thus increasing delivered loft.
Because there’s such a thing as too much of a good thing, reducing loft too much, for example by using excessive forward shaft lean or moving the ball back in your stance, tends to cause the ball to bounce because it is being driven into the putting surface at contact. This is also an undesirable result, because it starts the ball on its path in an unstable mode.
Of the factors other than impact force that affect the launch condition of a putted ball—delivered loft and the friction conditions of the putting surface—the one that the golfer can control is delivered loft. Based on proven studies, and my own personal experience, the first step is to reduce the loft on your putter (you can experiment with it, but –1˚ is a good starting point) and you can make adjustments, as conditions warrant, by varying the placement of the ball with respect to the vertical arc of your swing.
I started this article series with the intention of discussing why, like crying in baseball, there is no spin in putting—and why that spinning ball video clip on Instagram was a pointless demonstration based on misconception and ignorance. The scope of the article grew as I wrote, and then it split into two, despite my having held back a great deal of detail that I could have included.
I hope that I have been able to educate the reader a bit about the realities of an important aspect of putting—how the ball transitions from a static position to forward roll—and also in how you can go about maximizing the roll quality of your putts for more consistent distance control. (The importance of speed—and therefore distance control—was the subject of another putting article that I wrote about four years ago. My how time flies.)
Maybe if I get ambitious at some point in the future, I will take on the subject of the break.
—————————————————————————* As I mentioned, briefly, in the previous article, gravity affects the ball when the putting surface is slanted, but that is a subject for another discussion.
** Jeremy Pope, David James, Paul Wood, and Erik Henrikson, The effect of skid distance on distance control in golf putting (The 2014 Conference of the International Sports Engineering Association)
† I see you counting on your fingers, and yes, that’s only fifteen greens. The other three holes, including my nemesis, #6, are better not spoken of.
No comments:
Post a Comment