SCOTT SIMON, HOST:
You know the feel of a good putt.
(SOUNDBITE OF GOLF CLUB HITTING GOLF BALL)
SIMON: The golf club taps the ball just right. It rolls gently toward the hole at just the right speed, and you can hear the crowd begin - oh, no. The ball clips the rim. Spins away. Or worse, it goes into the hole only to roll back out. What is this nasty bit of physics known as the golfer's curse or the lip out? John Hogan is professor of applied mathematics at the University of Bristol. He's also the co-author of a new article published in Royal Society Open Science and joins us now. Thanks so much for being with us.
JOHN HOGAN: Glad to be here.
SIMON: Do you play golf, by the way?
HOGAN: Not at all.
SIMON: If I might begin this way, why was this important to you to find out at all?
HOGAN: OK. So our study is all based in the area of mechanics, which is the motion of bodies under the action of forces. And increasingly, mechanics is used a lot in sport to try and understand phenomena. It's used in Hawk-Eye in tennis and that stuff. And I got involved initially in a problem related to basketball and then noticed that there are great similarities to the golf problem. Mechanics is kind of like the ugly sister of a lot of mathematics. People said it's all been done and we should be in quantum mechanics and celestial mechanics. But there's a lot of mileage in the old girl yet, and it's been a fun project.
SIMON: Now, you've attempted to understand two main, what I'll call manifestations, of the curse - the rim lip out and the hole lip out. Can you talk us through that?
HOGAN: Sure. When a golfer putts a ball, it rolls on the green. But when it encounters the whole rim and starts to roll along it, you get another rotation induced as the ball starts to pitch into the hole. So you have these two rotations which are going on. And basically, the fate of the ball is decided by a competition between these two rotations. Now, when they exactly balance, the ball rolls around the rim at a fixed speed, and it leans into the hole at a fixed angle. And this is what we call the golf balls of death.
SIMON: Good lord, that's a dramatic term.
HOGAN: (Laughter) And then if the rolling dominates the pitching, the ball can still go a little bit round the rim of the hole, but then it flies off onto the putting green.
SIMON: Yeah.
HOGAN: And that is the rim lip out. But if pitching into the hole dominates, then either you have a successful putt, or you can have this very nasty thing called a hole lip out, where the ball is rolling on the inside of the hole now. And its potential energy - 'cause it's high above the bottom of the hole - is converted into spin, and it has a sort of pendulum motion, and it comes back out again. It's a bit like a skateboarder when they drop into a half pipe or something. They come back out the other side.
SIMON: Forgive me. All I do is play putt-putt golf with our daughter sometimes. Is this going to help me?
HOGAN: I would say that - I mean, certainly my golfing friends tell me this sort of thing happens when you hit the ball too hard. So the first thing I'd say is don't hit the ball too hard. The second thing I'd say is, you know, a golf hole, it has to be 4 1/4 inches wide. That's the standard width of all golf holes. None of these problems happen in the middle. So if you go there slowly and you get close to the center of the hole, you'll be fine.
SIMON: Well, that sounds easy.
HOGAN: (Laughter) Much easier said than done. I'm in awe of golfers, how they imagine to get anywhere near the hole.
SIMON: With respect, was this a problem that needed a solution?
HOGAN: I'm retired. I'm emeritus. It's a completely curiosity-driven thing. Having said that, you know, in the U.S., golf is - I got an economic activity rated to be about a hundred billion a year. And given that 40% of golfing shots are putts, more people could join in, get involved. Personally, I was driven from a curiosity perspective.
SIMON: John Hogan. His new research article is called - what a title, "Mechanics Of The Golf Lip Out." Practically trips off your tongue, doesn't it?
HOGAN: Absolutely. Transcript provided by NPR, Copyright NPR.
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