15 June 2014

Torque that Brazuca!

The first two goals in Switzerland's 2-1 win over Ecuador gave us great banana kicks from the left side into the penalty area.  The assists were every bit as spectacular as the headers that provided the goals.  Both relied on left-booted kicks that put clockwise spin (as seen from above) on the ball.  The left-to-right curve due to the the Magnus force meant the ball had a component of its velocity away from the goal and toward the waiting head of a teammate.  Both kicks were things of beauty!

Ecuador's Walter Ayoví kicked the ball by swinging his left leg across and upward.  Look at the image below (click on image for a larger view).
What a great image!  Notice the body lean.  The planted right boot pushed on the pitch to the right (as we see it in the image).  The pitch, by Newton's third law, pushed the right boot to our left.  That created a torque in the clockwise direction (again, as seen by us), which nicely balanced the counterclockwise torque created by Ayoví's weight.  That weight torque was clearly present because Ayoví's center of mass was not over his feet.  Enner Valencia was set up perfectly.

By swinging his left boot across Brazuca, Ayoví created the necessary torque to get the ball spinning.  That same type of torque was put on Brazuca by Ricardo Rodriguez of Switzerland as he sent the ball into the penalty area on a corner kick so that Admir Mehmedi could head in the equalizer.  I cropped the image below from my video feed (click on image for a larger view).
The net partially obstructs the view, but you should be able to see the body lean and Brazuca coming off Rodriguez's left boot.  Like the previous kick, boot must meet ball left of center as seen by the player.  A nonzero lever arm distance from the contact point to Brazuca's center of mass is necessary to get the ball spinning.

I can't leave this Sunday of World Cup action without commenting on the incomparable Lionel Messi.  After incredible footwork to get to one of his favorite spots on the pitch, Messi took advantage of an opening to send the ball off the left post and into the goal.  Look at the image below (click on image for a larger view).
Another left boot, but this time the line of force from the boot went above Brazuca's center of mass.  Messi's left boot is moving upwards in the above image.  Messi's genius was on full display not only in getting to the perfect spot for a shot on goal, but knowing to give Brazuca topspin.  Messi kicked the ball from 18 yards out, right on the center of the line for the penalty area.  The ball stayed low, and bounced just before hitting the left post.  There was no way the goal keeper could get such a shot.  The topspin meant there was a Magnus force pointing down, which helped keep the ball low to the pitch.  Watch that goal, and be amazed at one of the best to ever play the beautiful game.

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