21 March 2012

Lionel Messi -- Stability and Greatness!

By now the sports world has learned that Lionel Messi became the all-time leading scorer for Futbol Club Barcelona.  Messi earned the record in style with a hat trick last night against Granada.  Click here for an ESPN story and video highlights of Messi's three goals.  There is some great physics behind what Messi does on a football pitch!  All players are, of course, constrained by the laws of physics, but Messi is a fantastic player to watch when trying to understand the crucial role played by physics in goal scoring.  I have no idea how much physics Messi understands, but it is clear watching him that he has assimilated physics principles into his technique.  It is also clear that Messi has great teammates who are often able to get him the ball in what looks to be the perfect place.

Consider the first goal at the 17-minute mark.  On the above video, look at the footage near the 0:10 mark.  Messi was waving for the ball with his right hand just before entering the penalty area.  The ball reached him perfectly at about 5 yards (4.6 m) into the box.  Because Messi was right of the goal, he rotated his body counterclockwise (as seen from above).  When his left boot made contact with the ball, Messi was leaning slightly to the right, thus maintaining stability by ensuring that a net torque did not rotate him toward the ground.  Messi's left foot crossed in front of his body as he struck the ball, but his rightward lean kept him stable.  The ball struck the post on the left side of the goal and ricocheted in for the goal that tied the Barcelona record.

For the goal that set Messi apart from all Barcelona players, go to the 0:31 mark of the video where the game was in the 67th minute (was Messi offside?).  Messi was around 10 yards (9.1 m) from the goal.  Watch what happened when Messi received the ball with his left boot.  To maintain stability while his left leg was raised, Messi leaned back slightly, and you will note that both his arms were raised out from his sides.  By having his arms out, Messi was able to control any possible side-to-side motion that might have resulted from an unbalanced torque while his left boot dealt with the ball.  By moving his arms out, Messi increased his moment of inertia, which increased the torque required to tip him over.  If you freeze the video just right, it almost looks like Messi was doing the crane from Karate Kid, though his arms were not raised as high as Daniel's were (click here if you don't know what I mean).  Messi then booted a slow rainbow kick over the goal keeper, who was only about 3.5 yards (3.2 m) in front of Messi at the time, that sneaked into the left side of the goal.

For the goal at the 86-minute mark that earned Messi the hat trick, go to the 0:55 mark of the video.  Messi received a perfect pass 9 yards (8.2 m) from the goal line and 6 yards (5.5 m) right of the right goal post.  Mess first made contact with the pass with his left boot while his left leg was extended well in front of his body, a necessary move to arrest the motion of the pass.  Again, phenomenal stability was maintained because Messi's right leg was extended well behind his body.  He thus made sure there was not net torque to cause him to slip.  Messi then did his magic by eluding the goal keeper and getting to nearly the deepest part of the rightmost portion of the goal area.  Having rotated his body counterclockwise (as seen from above), Messi was able to gently guide the ball into the goal with his left boot moving in front of his right leg.  Just at the point of striking the ball, you will see Messi's lower legs almost making an X shape with his knees slightly outward.  Once again, complete stability!

There are many great players, past and present, that one may use to learn about the physics of great football.  For me, however, Lionel Messi is the paragon I use to see wonderful physics in the beautiful game.

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