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Picture this: It's the 18th hole and the game's on the line. You line up your putt, take a breath, and roll the ball toward the hole. The pace is firm, the line looks good—until the ball dips in, then cruelly pops back out onto the green. New research led by the University of Bristol has looked at the physics of what's known as the golf lip out.

A sporting quirk that affects both seasoned pros and amateur players alike, the lip out putt sees the ball hit the edge (lip) of the hole but fail to go in and instead roll away without dropping in.

Emeritus Professor John Hogan from the School of Engineering Mathematics and Technology at the University of Bristol decided to take his knowledge of mechanics and apply it to the 'lip out' phenomenon. The study is published in Royal Society Open Science.

Professor Hogan had dubbed these rogue golf balls 'the golf balls of death,' referencing the way they resemble motorcycle riders performing the circular 'wall of death' stunt.

"We considered the motion from the point of view of mechanics," Professor Hogan said. "We showed analytically there are two distinct types of lip out: the rim lip out where the center of mass of the golf ball does not fall below the level of the green, and the hole lip out where it does."

At the heart of both lip outs is a family of 'degenerate saddle equilibria' of the dynamics on the rim, according to Professor Hogan. This refers to the balanced point where the golf ball is teetering on the rim of the hole. It's not falling in but not safely resting on the green either—it is right on the edge.

The rim lip out sees the ball rotate around the top of the golf hole at a fixed angle and velocity, and a perturbation—another factor such as a grain of sand, a puff of wind, or the slightest spin—can affect whether the ball ends up either back on the green or sinks into the hole for a successful putt.

Meanwhile, the hole lip out only occurs in a small set of conditions. Professor Hogan explained, "Here the golf ball falls into the hole, where it undergoes a pendulum-like motion, as it rolls around the wall of the hole. Its potential energy is converted into spin, and then, provided the golf ball does not touch the bottom of the hole, it can return to the rim and back onto the green again."

So—how should golfers adjust their game? Well, that bit is easier said than done.

Professor Hogan said, "My golfing friends tell me that lip outs occur when you hit the ball too hard. Our research has showed that you need to aim as close to the center of the hole as possible, and to arrive at the rim of the hole with little speed.

"That combination means that the small amount of momentum the ball does have is just enough to tip the ball into the hole, and not enough to carry it around the rim and back onto the green."

Professor Hogan's work focuses on mechanics, the motion of bodies under the action of forces. Sir Isaac Newton used his Laws of Motion to study the motion of planets and now increasingly those principles are being applied to relevant sporting scenarios.

This research builds on Professor Hogan's previous work applying mechanics to sporting actions, having previously studied the physics behind skateboarding and the motion of a basketball after it hits the hoop.