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[Gene GeRue <genegerue AT ruralize.com>]

Best Way to Skip a Stone, The
+ISMFrench scientists used a robot to determine the optimal angle for stone 
skipping. But a human still holds the record of 40 skips.
By CLIVE THOMPSON

Published: December 12, 2004

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.

See: http://www.riverromp.com/skipping/steiner.htm

 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.''

http://www.nytimes.com/2004/12/12/magazine/12BEST.html