The science of juggling

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Barry Sperling usually has his hands full. An avid juggler for 16 years, he tosses balls into the air for fun and relaxation, hoping to catch and toss them again."Juggling allows me to be in a different world and forget my troubles," he says. "It's something you can do by yourself. You don't have to have an audience."Mr. Sperling, who lives in Alexandria, is a member of the Fairfax Jugglers. The club typically meets Thursday nights at Key Intermediate School in Springfield.

Though many jugglers never consider the scientific principles governing their activities, mathematics and physics are at the heart of the hobby.

The body has a comfort with the rhythm of juggling, Mr. Sperling says. Objects follow a mathematical curve when they are thrown into the air, and jugglers don't need to look at the entire curve or path of the object. When the juggler looks at the top of the curve, the brain can figure out where the ball or club will come down.

"Good jugglers don't look at their hands at all," Mr. Sperling says. "They never see the catches. They just feel them. If you get really good at it, you can go completely on the feel of it and juggle blindfolded. The hands will make all the adjustments that are necessary."

The mathematical theory of juggling is referred to as siteswap, says Andrew Conway, a former board member of the International Jugglers Association, based in Carrollton, Texas. He lives in Freeport, Grand Bahama.

In the late 1980s, jugglers Bruce Tiemann and Bengt Magnusson created a juggling notation based on the changing places of balls when juggling, he says.

Siteswap theory allows strings of numbers to represent a juggling pattern, Mr. Conway says. The number given to a throw is the number of beats later that the ball lands in either hand.

A common three-ball pattern has a siteswap of three (3, 3, 3), he says. When each ball is thrown, it lands three beats later, he says.

In one four-ball pattern, such as 3, 3, 6, the right hand throws a ball that lands three beats later. The left hand throws a ball that lands three beats later, and the right hand throws a ball that lands six beats later. The fourth ball, which previously was thrown by the left hand, would be in the air. Then the pattern repeats, starting with the left hand.

"You can be throwing it under the leg, behind the back, bouncing it off the floor," Mr. Conway says. "It doesn't matter. It's not in the scope of the notation. It's just when it leaves your hand and when it gets back again."