Rogue Waves

The Best Way to Skip a Stone

This was one of my favorite essays I wrote for this year’s New York Times Magazine issue on the “Year in Ideas” — about scientists who deduced the optimum way to skip a stone:

The Best Way to Skip a Stone

by Clive Thompson

Want to break the stone-skipping record? Here’s a hint: throw the stone at an angle of precisely 10 degrees to the water. That’s what a team of French scientists discovered when they constructed a machine to determine the ideal technique. Lyderic Bocquet, a physicist at the Universite Claude Bernard Lyon, became interested in the mechanics of skipping two years ago, while out tossing stones with his son. ”He asked me, why is the stone skipping and not sinking?” he recalls. Bocquet realized that while stone skipping had been around since the ancient Greeks, no scientist had ever deduced the ultimate equations for mastery. He wrote a short paper pondering ”the stone-skipping problem,” whereupon a fellow physicist, Christophe Clanet, suggested they solve it with the aid of a robot. They went on to create a device that could whip metal disks at a tank of water with utter precision.

As they began blasting away, the scientists quickly noticed something remarkable. No matter how fast or slow their robot threw, the disks always seemed to skip farther if the stone hit the water at an angle of roughly 20 degrees. Why? In a January paper for Nature, titled ”Secrets of Successful Stone-Skipping,” they concluded that this was because such an angle produced the briefest impact with the water and thus the least drag on the stone. Armed with this knowledge, they could figure out how to break the world record — a bouncy 40 skips, set in 2002 by Kurt Steiner. They began pitching stones faster and faster, but at its top performance, the robot could only manage 20 skips. ”It was vibrating, and pieces were falling off it,” Bocquet says. Nonetheless, the experiment this fall gave them the answer they needed. To achieve a record-breaking 41 skips, you’d have to throw a stone four inches in diameter at 60 miles an hour and at an angle of 10 degrees. You’d also want to perform this trick on a glass-smooth pond, since the scientists’ tests were conducted in a perfectly still experimental tank.

The scientists admit that there is probably no practical use for this knowledge. For his part, Bocquet admits that he can’t manage more than 15 skips himself. ”Going from theory to practice,” he says, ”is still difficult.”

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I'm Clive Thompson, the author of Smarter Than You Think: How Technology is Changing Our Minds for the Better (Penguin Press). You can order the book now at Amazon, Barnes and Noble, Powells, Indiebound, or through your local bookstore! I'm also a contributing writer for the New York Times Magazine and a columnist for Wired magazine. Email is here or ping me via the antiquated form of AOL IM (pomeranian99).

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