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Skipping Stones

Want to be an expert stone skipper? Learn how on this Moment of Science.

As everyone who has had the pleasure knows, flinging the right stone at just the right angle with the right amount of spin can send it skipping across the surface of a lake or any other still body of water. The physics of the thing are simple.

Basically, the size, shape, and spin of the stone determines how successfully the water’s surface is able to resist and push back when the stone lands. The best skipping stones have flat surfaces; when the stone hits the water at a relatively flat angle, its weight is spread across much of its surface and encounters a lot of resistance from the water. Conversely, when a spherical or jagged rock hits the water, the bulk of its weight is focused in a smaller area, causing it to break through the water’s surface with more force.

The trick to getting the stone to keep skipping after the initial bounce is the spin. Throwing the rock so it spins creates a gyroscopic effect, much like how a spinning top can balance on a point until the spin peters out. As long as it keeps spinning, the rock stays flat. When the spin stops, the rock tilts forward and breaks through the water’s surface.

The world record? An amazing thirty-eight skips by Jerdone Coleman-McGhee of Texas in 1994.

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