Skipping Stones Is No Longer Just Child’s Play

How do you get the best results when skipping stones across a small pond on a summer’s day? Spin the flat stone, throw it as hard as you can and hit the surface at an angle of 20 degrees, according to French researchers.

Skipping stones is a tradition that goes back thousands of years, and the rules have not changed over time. The goal is to see how many times you can get the stone to bounce.

Physicist Christophe Clanet and his colleagues at a research institute in Marseilles constructed a device that would reproducibly launch a flat metal disk at a container of water, allowing them to independently vary throwing speed, rotation and angle of attack. Impacts with water were filmed with a high-speed video camera.

Their observations, reported in the Jan. 1 issue of Nature, will probably not be surprising to practitioners of the art.

They found that disks -- or stones -- hitting at an angle greater than 45 degrees do not bounce. Instead, they enter the water.

Disks encountering the surface at a very low angle do bounce, but they remain in contact with water for so long that much of their energy is dissipated. The researchers concluded that the “magic” angle of about 20 degrees provided the minimum time of contact with the surface and the maximum number of bounces.