When a tied soccer match goes to penalty kicks, suddenly it's an entirely different game -- especially when players like famed Portuguese forward Cristiano Ronaldo step up to unleash zigzagging shots on goal.
Much like the knuckleball in baseball, these shots are nearly impossible to predict. Now French researchers are shedding light on this mystery with their unique kicking machine.
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The "knuckleball" characteristic, where a ball that has minimal speed and spin moves in unpredictable ways, is only seen in a few sports: baseball, volleyball, and soccer. To explore the phenomenon, scientists from the École Polytechnique's Hydrodynamic Laboratory and the engineering school ESPCI ParisTech in Paris developed a machine to reproduce it with a soccer ball.
Led by researcher Baptiste Darbois Texier, the team constructed the kicking machine from an electric motor, a steel arm, and a flat plate, they explained in an article published in the New Journal of Physics. The machine allowed them to launch balls with little spin. Each shot's trajectory was captured by a high-speed camera and measured in a wind tunnel.