![]() ![]() Truscott declined to say precisely what the U.S. The program was only rarely used but successful, breaching two dams in Germany's Ruhr Valley in 1943. In the 1940s, the British developed the Wallis bouncing bomb, a surface torpedo that could be dropped from a plane and skipped across the surface of a lake to breach dams otherwise protected by underwater torpedo nets. These skipping cannonballs required less precision to make a hit, and tended to bounce up on decks, knocking off enemy sailors and breaking masts. For example, in the 1800s, Truscott said, sailors would angle cannonballs to skip over the water rather than lobbing them high through the air. In Naval history, there are several examples of projectiles that skip over water rather than traveling through it or above it. ![]() The question of the water-bouncing ball isn't purely academic - or purely fun. Instead of an angle of 20 degrees, the Waboba can hit the water at up to 40 degrees and still bounce, he said. You still have to get the correct speed and angle for a bounce, Truscott said, but even a "really sloppy" throw gets impressive results. The elasticity of the ball means the thrower doesn't have to worry about the rotation, as they would with the stone. In fact, that cavity made by the ball forms slower than the ball moves, Truscott said, which creates a little water slope, much like a ski jump, that the ball can use on its upward climb. The change in shape increases the surface area of the ball, increasing its lift force by a factor of four, which propels it out of the water cavity it creates as it hits the surface. When the ball hits the water surface, it deforms, flattening like a pancake. They found that the key is in the ball's elasticity. To find out why the ball bounces so easily, Truscott and his colleagues set up high-speed cameras and shot the balls out of potato guns, which use a length of pipe and a burst of air to propel a projectile. ![]() Truscott compares it to a performance-enhancing drug for skipping. But the Waboba takes much of the skill out of the equation, making it easy to get 30 or 40 bounces without much practice. Most people can skip a rock just a couple times, Truscott said, and a few can achieve 10 or so. The record in the Guinness Book of World Records for most skips was set in 2007 by Pennsylvania man Russell Byars, who skipped a stone a stunning 51 times. This rotation gives the stone stability, allowing it to hit the water at the correct angle - 20 degrees for the maximum possible skips. The physics of rock-skipping is fairly easy to explain: You need a flat rock thrown with the perfect rotation. Like many people, Truscott and his son enjoy trying to skip rocks across smooth water. ![]()
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