September 24, 2016

Science of soccer, Webster soccer player finds an advantage through the flip throw

Lauren Pratt, three time All-Conference team selection and 2012 Newcomer of the Year supplied the Webster University Women’s Soccer team with unexpected talent and success. But it was her flip throw-ins that surprised her teammates and anyone who saw her perform it.

 VIDEO BY SAM MASTERSON

The only thing Lauren Pratt thinks about when she takes a throw-in for the Webster University women’s soccer team is to land back on the ground. She runs toward the touch line and tightly grips the ball as she places it on the ground. Then her heels fly over her head and muscle memory takes over when her hands come back over her head. Finally, with a perfectly-timed release she executes a flip throw-in.

Pratt gets dizzy if she repeats the throw too often and lumbar problems limited her use of the flip throw in the 2013 and 2014 seasons. But her acrobatics have led to conference awards and championship winning goals.

In the 2012 St. Louis Intercollegiate Athletic Conference (SLIAC) Championship, Pratt’s flip throw led to the game winning goal. Webster practiced the play often, and it was designed for Pratt to take the throw and find the team’s tallest player, Kristen Montgomery, in the 18-yard box. She flicked the ball back toward the goal where teammates like Ally Nikolaus volley the ball out of the air and past the opposing goalie.

If Pratt had used a normal throw-in that goal may not have happened. Her average throw travels near the edge of the 18-yard box or 59 feet. But a flip throw allows her to land the ball near the penalty spot with an average distance of 77 feet.

 

Photo contributed by Randy Schield Webster junior Lauren Pratt executes her flip throw during a game in 2013.

Photo contributed by Randy Schield
Webster junior Lauren Pratt executes her flip throw during a game in 2013.

Webster physics professor Ravin Kodikara explained her added distance through the additions of velocities formula.

Kodikara said Pratt uses her entire body as an extension of her arms to put a force on the ball in a certain direction. In a normal throw, she uses just her arms and shoulders to throw the ball, but her flip throw allows her to rotate in mid air around her center of gravity.

“Let’s say you throw a piece of wood down a hallway,” Kodikara said. “It will rotate around the center of gravity. So when the body rotates around the center of gravity that rotation adds some speed to your movement.”

To find a final velocity using the additions of velocities formula you add each angular velocity together. The angular velocity is found by dividing the change of the angle by the time it took. So if Pratt moves her arm 40 degrees in two seconds her angular velocity is 20 degrees per second.

Since there are so many body movements needed to perform the throw, there are many things that can go wrong. Head Coach Luigi Scire compared Pratt’s flip throw to an opponent of Webster’s who could also perform a flip throw. But Scire said the other player was not as effective as Pratt.

“If you don’t do it properly it comes up and floats into the box,” Scire said. “Her’s was not like Lauren’swho comes through on it kind of like a frozen rope and it has a purpose and that purpose is to find Kristen (Montogmery’s) head and flick it behind the defense. When she does it correctly, it comes through very quickly and it is very hard to defend.”

VIDEO BY SAM MASTERSON

The Webster Men’s Soccer team has multiple players with long throw-in abilities. Forward Kris Brown’s average throw-in was 107 feet, nearly twice as long as Pratt’s normal throw. But Brown is 6 feet tall and Kodikara said that height along with stronger arms than Pratt allow him to create a higher velocity during throw ins. Pratt’s arms are 2 feet 1 inch long compared to Brown’s arm length of 2 feet 6 inches.

Kodikara said that difference can be explained through finding the linear speed of the ball. The distance of the ball from the player’s center of gravity has a big effect on linear speed.

 

“Let’s say Kris (Brown) and Lauren (Pratt) can move their forearms at the same speed or they have the same angular speed,” Kodikara said. “But Kris has a longer forearm so he gets a higher final speed. So there is an advantage height wise.”

But Kodikara said Pratt’s height gives her the advantage over Brown if he wanted to learn a flip throw. Kodikara said because of Brown’s longer torso he would have to deal with more rotational inertia than Pratt in a flip throw. Rotational inertia is force on the ball opposite of its desired movement around an anchor point, or in the case of a flip throw, the center of gravity.

VIDEO BY SAM MASTERSON

Brown said he wouldn’t even be able to flip throw if he wanted to.

“I’ve always tried to do it but never able to and it’s crazy,” Brown said. “It’s a huge advantage for the girls team to have it.”

 


VIDEO BY SAM MASTERSON

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