Physics of Football: Pirlo's free kick

Andrea Pirlo was born in Flero (Italy) in 19 May 1979. From a young age, he shows great football skills that have given him the deserved nickname of "Maestro" of football. His game reflects an amazing technique; Pirlo is rightly considered as one of the best midfielders in the history of Italian and international football. His specialty are the free kicks, the curse of goal keepers. Not surprisingly, Pirlo's free kick has been defined: "La Maledetta" (the Cursed Free kick).

Andrea Pirlo, nicknamed the Football Master

Let's analyze the physics of this football prowess.

La Maledetta is a type of trajectory that Andrea imparts to the ball. The ball, in fact, suddenly lowers, after the barrier, and tricks the goalkeeper. How does he manage to make the ball bend in this way? Another Master offers us the answer we are looking for. The Bernoulli equation shows that by increasing the velocity of the air particles, the pressure exerted on the lower surface of the ball decreases. By striking the ball above the center of the sphere, Andrea gives the ball a rotation from top to bottom. Thanks to the air resistance, the particles that are near the surface of the ball are dragged in this rotational motion. As a result, the air below the ball will travel faster than the air above the ball. Therefore, a resulting force is produced, directed downwards, which tends to increase the curvature of the trajectory towards the ground.

The Magnus effect

Leaving aside now the Magnus effect (neglecting, therefore, the resistance of the air), we explain how a normal Andrea's freekick proves to be a challenge for the goalkeepers. Assuming that Andrea kicks the ball with an inclination of 40 ° to the ground and that is at a distance of 28 meters from the door, the ball reaches the door after 2.15 seconds from the bar, slipping into the net at a height of 0.813 meters. Considering that the average reaction time of a normal person is equal to 0.250 seconds and that the goal keeper sees the ball after it has passed the barrier, the goalkeeper has only 1,136 seconds to save the ball. In order to touch the ball, the goalkeeper should jump at a very high speed!

The goalkeeper sees the ball only after it has passed the barrier. Its reaction time is 250 thousandths of a second.

Of course, in order to create these conditions, a player needs a superfine technique to be able to direct the ball towards the door in this way. By combining these two synthetic considerations, we briefly showed how Andrea's specialty is in name and in fact Cursed for the opponents.

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