14 June 2014

To Spin or Not to Spin?

The two goals scored in the first half of Italy's match with England were great, both from a strategic point of view and from physics point of view.  Claudio Marchisio scored the match's first goal after Italy executed a perfect corner kick play.  Instead of powering the ball into the penalty area, Marchisio received the ball after some fancy and tricky footwork from teammates.  He then kick the ball low to the pitch with almost not spin.  Check out the image below (click on image for larger view).
The image I cropped from the video feed I was watching shows the ball low to the pitch with very little spin.  Note how clear the ball is compared to the players.  Marchisio's shot looked to have a slight knuckle effect, which I estimate from one replay that showed the shot from the back of the goal.  At the speed and angle of the launch, the ball would not have laterally deflected more than about 2% of its horizontal range (from boot to the first time the ball hit the pitch).  He opted for no spin because he was after a straight shot on goal.

England tied the match just two minutes later when Wayne Rooney found Daniel Sturridge with a beautiful cross off his left boot.  The ball had lots of clockwise spin (as seen from above), which meant it curved left to right as Rooney would have seen it.  Look at the image below (click on image for a larger view).
Rooney is off to the right, out of frame of the video feed I cropped.  His perfectly placed ball is heading for Sturridge.  The ball's spin meant that it arced a little toward Sturridge, which made for easy handling by the forward.

The first half goals showed when it's good to kick with little-to-no spin and when a lot of spin is needed.  Great physics on those two goals!

Italy got the winning goal on a well-timed header by Mario Balotelli just five minutes into the second half.  An excruciatingly close miss by Rooney and several errant kicks by England late helped Italy close out a 2-1 win and three very big points on the heels of Costa Rica's stunning win over Uruguay.

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