Sunday, December 06, 2009

Putting on Windy Greens

The 30-second takeaway message is wind at the surface of the green matters once your pants legs are flapping, and the golfer should learn the effects of strong winds by discriminating among headwinds, tailwinds, and crosswinds, as well as strength or wind speed perception and steadiness and its effect on long and short putts on slow and fast surfaces in terms of line and distance and how to play breaking putts. Surface wind is similar to slope and grain, with headwinds having the most pronounced effect on putts and any wind having the most effect when the ball is rolling slowly.

Conventional golf lore teaches that when the wind is strong enough to challenge balance, the golfer can "take in sail" by setting up in a low and compact posture with wider stance and a lower and tighter grip, and use a more decisive stroke, but the skill of appropriately playing the wind is much more than this adjustment of setup and stroke! The golfer needs to know what the wind will do to line and distance.

How the air density, direction and speed affectts the rolling ball is a bit of a trick. The cross-sectional area of the ball and the wind-ball relative directions and speeds of ball into wind create a high pressure resistance on the front of the ball and a low pressure "drag" behind the ball that is like attaching a tail to a kite or a tail-fin to a glide plane. This added "tail " or "drag" both slows the ball down and also directs the ball's path into the wind's direction. The more direct the ball roll into the wind, the greater the "drag", so sidewinds and various crosswinds create some pressure against the ball's cross-sectional area, but the relative ball-wind speed in these cases results in not so much "drag" along the ball's line of roll as happens when the ball heads straight into the wind and the net result is a smaller effective "drag" located between the wind direction and the ball direction. A little paradoxical is the cross-effects of ball speed in wind: the faster the ball rolls, the greater the "drag" slows and steers the ball, but also the faster the ball the less time the wind has to affect the roll.

Consequently, wind acts like break and grain at once. Wind effectively sticks a dab of mud ("drag") on the ball that imbalances it the same way slope imbalances a ball, and the mud dab "turns" the ball's roll according to the location of the mud and its size. That's what slope and gravity do also. Tailwinds less than the ball speed reduce the size of this mud and tailwinds faster than the ball effectively sick a dab of mud on the front area of the ball. Balls rolling directly in line with a headwind get slowed down, but also get steered to stay on line more than balls rolling in calm air or the same wind coming directly from behind.

For the wind influence on ball direction, perhaps a better image is that of the wind vane. Wind for direction X influences ball rolling in direction Y by "steering" the ball onto the wind's heading, the same way the wind steers a wind vane. The tail of the vane with a dab of mud both influence the direction of the roll similarly. The magnitude of the influence and the effect on the actual curving path of the ball depend upon the relative forces of wind and ball, given their speeds and directions and the density of the air.

The "effect" wind has on a rolling ball will depend upon the total sum of instantaneous effects of wind vector (both speed and direction of speed relative to the ball) and the ball vector at each point along the path. Hence, the longer the wind operates before the hole is reached, the greater the effect. Playing less break in the wind is similar to keeping an iron show "below" the wind, but there is a limit of how fast the ball's delivery speed can be played before the trade-off becomes negative. Sometimes, the golfer should simply accept the wind and play the wind as it is. The real trouble comes from changeable, gusting winds. That's like playing a green with the surface contour and slope or green speed changing right after you start the ball rolling!

For MUCH more about wind, perceiving and measuring wind speed and direction, and how to take this into account on the greens -- complete with video examples and tools for the knowledgeable golfer -- visit this webpage on the PuttingZone.


Geoff Mangum
Putting Coach and Theorist

"The best putting instruction book in golf history" is now available for purchase as an ebook download: Optimal Putting: Brain Science, Instincts, and the Four Skills of Putting (2008, 282-pages, only $9.95).

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