Which one of us, finding ourselves near a large body of calm water, has been able to resist the temptaion to indulge in the delightful activity of trying to skip stones across the surface? The number of skips that I am able to get before it sinks is three, maybe four. So it is a pleasure to see world champion Keisuke Hashimoto in acction. His wind up alone is thing of beauty. (Via Rusty Blazenhoff)
(To see the above, follow the link that the ‘video unavailable’ window provides.)
But he is still mortal and doesn’t always succeed.
This article discusses the science of stone skipping.
[I]n February , the American Journal of Physics published “a simplified description of the collisional process of the stone with water” by Lydéric Bocquet. Bocquet is a physicist at Claude Bernard Lyon University in Villeurbanne, France…. With each skip, gravity pulls the stone deeper under the surface, and the water exerts more drag on the stone. Eventually, the drag becomes so great that the stone can’t break free. A skipping stone spends 100 times longer in the air than it does on water, but air is 1,000 times less dense than water, so its effect on the flight is relatively minimal.
The key to a good skip, Bocquet says, lies in spinning the stone. On the water, a stone’s spin keeps it poised on its trailing edge, rather than somersaulting. In the air, spin provides stability, as with a Frisbee. If the thrower gets the stone off to a bad start, spin can bring it into better position before it hits the water.
Bocquet has developed a formula for estimating how many times a stone will skip based on spin and speed. He calculates, for instance, that for a stone to skip five times it has to spin five times per second; to skip 15 times (Bocquet’s personal record), it has to spin almost nine times per second. According to this formula, McGhee’s world record-setting throw was spinning nearly 14 times a second and moving at nearly 40 feet per second.
This article discusses the technique of the person who held the Guinness record as of 2003.
To achieve such results, McGhee starts by picking through piles of stones, turning each one over and feeling its weight. He sets the flattest-looking candidate in the crook of his pointer finger, curling his other fingers beneath it. Then he stands up straight, wrist cocked high above his head like a flamenco dancer with castanets. This stance used to be an oddity—most stone skippers crouched low to the water—but it’s now widely imitated. Although McGhee starts with the stone held high, he releases it at his side, as parallel to the water as possible. “The more parallel you throw it, the less energy it uses to try to fly right,” he says.
Stones that aren’t perfectly shaped, and ones that have a little heft, seem to work best. Waves and gusts of air can send a light, nicely rounded stone off course. “You’d have a hard time skipping a cracker,” McGhee says.
There is no question that the science is going to be extremely complicated because it involves non-linear hydrodynamics involving two different media (air and water) and impulsive collisions.
Since this article was written in 2003, there may well have been improvements in the records and the scientific understanding of the skipping process since then.