18 June 2014

USA Corners Its Way to Win!

Two days have passed since I was jumping up and down after my home country defeated Ghana, 2-1.  Ghana has had our number in recent World Cups, so a win was sweet, and even more so given the quality of competition in our group.  The Wall Street Journal published today a little blurb I sent them on the corner kick that set up the winning goal.  I've only now had time to add a few more comments beyond what the Wall Street Journal published.

About four minutes following a great equalizing goal by Ghana in the 82nd minute, USA had a corner kick right of the goal as seen by someone looking at the goal from the middle of the pitch.  The image below shows Graham Zusi in the 86th minute about to deliver the corner kick (click on the image for a larger view).
He kicked the ball with his right boot, which imparted counterclockwise spin (as seen from above) on the ball.  He launched the ball at a speed of about 59 mph (95 kph).  The ball curved to his left, creating a perfect banana trajectory.  John Brooks headed the ball into the goal after the ball spent 1.47 seconds in the air.  The image below shows Brooks with Brazuca on his head (click on the image for a larger view).
The magnitude of the force Brooks exerted on the ball, which is the same magnitude force he felt from the ball, was nearly 120 pounds!  As great as Brooks's header was, I really love the corner kick that set it up.  Check out the trajectory below (click on the image for a larger view).
The solid red curve is the actual trajectory.  The red dashed curve shows the shadow on the pitch.  The dark thin curve is what the trajectory would have looked like has there been no spin on the ball, i.e. no banana kick made from whipped air using the Magnus force (that kick's shadow is also shown).  The real ball moved nearly 6 yards (5.5 m) laterally to the left.  Moving toward Brooks helped him with his header.  He could give the ball speed into the goal by almost reversing the normal component of the ball's impact velocity.

Isn't that corner kick a thing of beauty?

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