SHARPER SHORT GAME? HIT YOUR 12

THE SCIENCE OF 3 SHOTS: PROB­A­BLY MORE THAN YOU NEED TO KNOW, BUT HERE’S WHY THE BALL DOES WHAT IT DOES

Golf Digest (South Africa) - - Front Page - BY CAMERON MCCOR­NICK

When­ever we take a sig­nif­i­cant break from play­ing, it’s th­ese lit­tle shots that usu­ally ac­quire the most rust. Fig­ur­ing them out again is tough, be­cause there are so many ways to ex­per­i­ment with tech­nique. Un­like with the full swing, our no­tion of text­book form around the greens is less spe­cific.

That said, at the mo­ment of truth – im­pact – well-struck short-game shots are not mys­te­ri­ous, at least when viewed through the realm of physics. Us­ing a Track­Man launch mon­i­tor and my best stu­dents, I recorded data on three es­sen­tial shots: a green­side bunker shot, a low-fly­ing “skid-spin­ner” chip and a flop shot. I then shared this data with John McPhee, PhD, a mem­ber of the Golf Di­gest Tech­ni­cal Panel and pro­fes­sor of sys­tems de­sign en­gi­neer­ing at the Uni­ver­sity of Water­loo in Canada. We ex­am­ined the physics of suc­cess­ful shots and dis­cov­ered some com­mon el­e­ments, which we’ll share with you here. As com­pli­cated as the science might seem, a ba­sic un­der­stand­ing can re­ally help. The next time you’re grind­ing at the prac­tice area, you’ll at least know what you’re try­ing to do.

– WITH MAX ADLER & JOHN McPHEE, PHD

1. THE BUNKER SHOT

▶ MATCH YOUR SPEED TO THE MOIS­TURE

mcphee says:

On a green­side bunker shot that spins and stops quickly, there’s less sand be­tween the club­face and the ball. Think of the sand on the face as lay­ers that slide over one an­other. The fewer the lay­ers, the greater the trans­fer of shear­ing force to the ball ( see di­a­gram, F), which cre­ates more back­spin ( S).

Moist sand has higher shear strength than dry sand (this is why wet sand cas­tles can be built taller), so moist sand lay­ers can with­stand higher shear forces be­fore they slide. When sand is dry and pow­dery, more of the club’s en­ergy is spent on slid­ing the sand lay­ers than on im­part­ing back­spin to the ball.

mccormick says:

The take­away here is how to plan. With moist sand (not wet, heavy sand), you can try for back­spin. If the sand is dry, ex­pect more roll­out. We also see how crit­i­cal club­head speed or ve­loc­ity ( V) is. In our tests, I had to swing the club 103 km per hour to fly the ball 20 me­tres ( right). In dry sand, I had to swing 110 kph, or near my phys­i­cal limit with a wedge.

To get faster through the sand, swing to a fuller fin­ish. But if you’re a slow swinger, you’re bet­ter off ad­just­ing your club’s en­try point. The closer to the ball you en­ter the sand, the less you’ll be robbed of speed – and spin.

2. THE SKID SPIN­NER

▶ WHEN LOW ON THE FACE IS AC­TU­ALLY GOOD

mcphee says:

For this low chip that halts quickly af­ter its sec­ond or third bounce, the ball must be hit low on the club­face. This ro­tates the club­head clock­wise dur­ing im­pact ( see di­a­gram), which has two ef­fects: First, the club is de­lofted by the im­pact force, so the ball’s tra­jec­tory is low­ered. Sec­ond, be­cause the ball com­presses and rolls up the club­face, the clock­wise club ro­ta­tion cre­ates counterclockwise ball ro­ta­tion, known as ver­ti­cal gear ef­fect.

This dy­namic adds to the spin ( S) that re­sults from the club’s loft. The glanc­ing blow al­lows more of the club’s ve­loc­ity to go to­wards spin than speed.

mccormick says

This is such a fun shot. It comes off like a skull and be­wil­ders your play­ing part­ners when it sizzles to a stop. What we know is, you have to hit the ball low on the face – and a bit to­wards the toe helps. The key is to make a shal­low pass through the ball.

Widen your stance and feel that the club swings close to the ground, es­pe­cially on the fol­lowthrough ( right). This al­lows the club to skid through im­pact right where the bot­tom of the ball meets the ground to cre­ate a tan­gen­tial blow. You shouldn’t take a divot, so it’s eas­ier to achieve this shot off firm turf or when the ball is perched high on a bed of grass.

3. THE FLOP SHOT

◀ THE CLUB’S BOUNCE GOES UN­DER THE BALL

mcphee says:

On this shot, the ball is hit higher on the club­face with more di­rect im­pact than the skid spin­ner. The ball stops quickly on the green be­cause of its steep land­ing an­gle, not its back­spin. For Cameron’s 30-me­tre flop shot, the back­spin ( S) is only 4 100 rev­o­lu­tions per minute, but the launch an­gle is up to 51 de­grees.

The ball speed is sim­i­lar to that for the 30-me­tre skid spin­ner, even though the club’s ve­loc­ity ( V) is much faster. The rea­son is sim­ple: More en­ergy is go­ing into hit­ting the ground with the bounce of the club to cre­ate a slightly up­ward an­gle of attack on the ball.

mccormick says:

At ad­dress, lay the club­face so it points up to the sky. This open face, where you can see the lead­ing edge, cre­ates a high prob­a­bil­ity that you’ll de­liver max­i­mum loft. How, you ask, can you strike the ball high on the club­face when it’s open this much? At im­pact, the club’s sole is go­ing to push down into the ground to cre­ate room for it to slide un­der the ball. The key is fast wrists – and no ten­sion.

The wrists should hinge so that the club­head rises higher than the shoul­ders on both sides of the swing ( left). Feel that the club­face passes un­der the ball very quickly, like a spat­ula slid­ing un­der a pan­cake.

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