Why Physicists Love Super Balls – the coefficient of restitution

Super Balls are toys beloved by children because of their extraordinary ability to bounce. Physicists love them for exactly the same reason. Drop a baseball on the floor and it will hardly bounce at all. Drop a Super Ball from shoulder height, and it will bounce back 92 percent of the way to the drop-off point. Super Balls also are just as bouncy vertically as they are horizontally, and they spin oddly. “Physicists love it because it has interesting physical properties,” said Rod Cross, retired professor of physics at the University of Sydney in Australia, whose latest paper on Super Balls appears in the American Journal of Physics. His research also demonstrated the odd way all balls roll.

The Super Ball was invented and patented in 1964 by chemist Norman Stingley. The ball is made of a synthetic material he called Zectron, using a polymer polybutadiene and other materials, a form of artificial rubber. It was sold to toy stores by the Wham-O company and was, for a while in the 60s, a great fad. Almost 50 years later, it is still sold by Wham-O and it is possible to imagine that many of those sales go to physicists and physics students.

A Google Scholar search of “Super ball” returned 460,000 entries, including scientific papers, poster presentations, dissertations, and books. Bouncing Super Balls has become a standard physics demonstration, Cross said, and the papers are crammed with formulas, charts, and drawings. What entrances scientists is how well the balls bounce, an ability described in jargon as the coefficient of restitution, which depends on the elasticity of the surface. The Super Ball is almost perfectly elastic in both the horizontal and vertical directions. The Super Ball has an almost perfect coefficient of restitution and does things other balls do not. Edited from: Why Physicists Love Super Balls

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