In 1997, Brazilian midfielder Roberto Carlos carefully placed a soccer ball on the field for a free kick against France. He took a 5-yard running start, planted his right foot beside the ball and swung back his left. His follow-through took both legs sideways, and he landed and staggered slightly. The ball sailed 35 yards, bending around the wall of French defenders. It clearly appeared to be going wide right, and even a ball boy ducked. Then the ball swerved left and down to carom inside of the goalpost for a goal.
Kicking
More than a decade later, Roberto Carlos’s kick continues to fascinate physicists. In a 2010 report in the New Journal of Physics, a French team of scientists developed an equation to describe the ball’s path. And a trio of engineers and sports scientists analyzed it on the Institute of Physics website. Takeshi Asal, Takao Akatsuka and Steve Haake noted that Carlos, who practiced the kick all the time in training, intuitively knew how to curve the ball. The mechanics of kicking it to go straight require a straight-on kick with the instep in line with the ball’s center of gravity. If you kick the ball off center with the front of your foot and the angle between your leg and foot at 90 degrees, the ball will spin. A really hard strike causes air turbulence, more so when the ball is dry than wet. And while the type of soccer cleats worn affect the trajectory of the ball, “ultimately, however, it is the footballer who makes the difference,” the authors concluded.
Dribbling
Soccer mechanics require mastery at all levels, from Brazilian pros all the way down to soccer tots. A skill taught right away to the youngest players, dribbling involves using all parts of the foot and body except the arms and hands to advance the ball. Children often use just the inside of the foot to move the ball. If you coach young players, have them use the outside and top of the feet and drag the ball with the sole of the foot. These varied mechanics for dribbling set them up for the essential feints they need to fool opponents as they develop as players.
Heading
Players ages 10 and older can add heading to their game. Teach players to connect with the ball with their forehead where it meets the hairline “because a face ball hurts,” writes the authors of “Knack Coaching Youth Soccer.” The player needs to square her body to the ball, knees bent, eyes locked on the incoming ball. As the ball comes in, she must lock her head and neck in place and so the ball receives the power of the header from the entire body.
Running
Performance in soccer depends on acceleration, particularly to loose balls. Soccer and baseball conditioning coach Vern Gambetta breaks down the mechanics of acceleration in terms of posture, arm action and leg action. Body lean has to come from the ankle, not the waist, he writes in “Soccer Speed.” The arms need to drive down and back to help the body apply force against the ground. Each succeeding step needs to increase in stride until full stride length is attained. A key part of acceleration is a positive shin angle to the ground, meaning the shin of the forward leg during each stride is angled forward rather back in relation to the ground.
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