Physicists investigate soccer star Cristiano Ronaldo’s ‘Knuckleball’ shot

Cristiano Ronaldo, one of European Football’s most talented (and handsome) players, is known worldwide for a special kick. He calls it the “Knuckleball,” and like baseball’s knuckleball, Ronaldo’s kick dances unpredictably into the net, much to the frustration of opposing goalies.

Recently, physicists investigated the nature of Ronaldo’s famed “Knuckeball” shot, and it seems they have an answer that will demystify the kick’s odd trajectory. The team of researchers will reveal their findings at the American Physical Society’s (APS) Division of Fluid Dynamics (DFD) meeting, November 18 – 20, 2012, in San Diego, California.

“A soccer ball kicked at very low spin can exhibit a zigzag trajectory,” say the researchers in an abstract from the findings. “Along its straight path, the ball deviates laterally from about 0.2 m, that is to say one ball diameter. One zig zag happens as the ball travelled about 15 m. As the deviation direction seems unpredictable, this effect is highly annoying for goalkeepers.”

Researchers add, “That is why Cristiano Ronaldo and many soccer players are looking for this phenomenon. Those trajectories called knuckleballs are also observed on volleyball and baseball. We study experimentally indoor knuckleballs for different balls varying from soccer balls to smooth spheres.”

The researchers plan to show that the knuckling effect “doesn’t derive from ball deformations at foot impact or ball seams,” but from “aerodynamic lift forces on a smooth sphere are fluctuating and are responsible for knuckleballs.”

Watch Ronaldo’s “Knuckleball” in action. The goal is blocked but it has some crazy movement.