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By Jeff Z. Klein, New York Times
Soccer has been described as ''the beautiful game,'' a sport
that requires flights of magical improvisational genius. Take,
for example, free kicks, and the planet's best player at making
them, David Beckham of England. Beckham has mastered the art of
inducing the ball, from a standing start, to soar over a wall of
defenders standing 10 yards away and then seemingly contradict
the laws of nature by veering downward at the last second so
that it drops beneath the crossbar. It is called bending a free
kick, and until recently it was assumed that such mysterious
skill could be neither deciphered nor taught.
But this year an international team of researchers managed to
solve the mystery of how Beckham bends it -- and in so doing,
created the perfect model for the perfect kick. Engineers from
the University of Sheffield in England and Yamagata University
in Japan, along with researchers at an international
engineering-software company called Fluent, used high-speed
video analysis, computer models and wind-tunnel simulations to
determine the swirl of forces that guided Beckham's famous free
kick against Greece that propelled England into the 2002 World
Cup. Standing 29 yards in front of the Greek net, the
researchers say, Beckham most likely struck the ball about 80
millimeters (3.15 inches) to the right of center with his right
foot, sending it off at 80 miles per hour spinning right to left
at about 8 revolutions per second.
The ball rose over the wall of defenders, pushed leftward by the
sideways pressure, created by spin, that physicists call the
Magnus Force. But a few yards from the net, another force took
over: atmospheric drag. As the ball slowed, the researchers say,
the airflow around it suddenly shifted from ''turbulent'' to
''laminar'' (or in layman's terms, from bumpy to smooth). In a
split second, the drag on the ball increased by 150 percent, and
that caused the ball to plummet and dip just under the crossbar.
If Beckham had struck the ball with more spin, it would never
have cleared the Greek wall; too little spin, and the ball would
have sailed harmlessly over the net. ''Beckham was instinctively
applying some very sophisticated physics in scoring that great
goal,'' reports Matt Carre, an engineer at the University of
Sheffield.
So it's simple: kick the ball at just the right point, at just
the right speed, creating just the right spin, and you, too, can
bend it like Beckham. ''I believe that it would now be possible
to design an optimum free kick for any given point,'' Keith
Hanna of Fluent says. Of course, designing the ultimate kick and
actually performing it on the playing field are two different
things -- and that difference is what keeps the beautiful game
beautiful.
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