## MatheMUSEments

Articles for kids about math in everyday life, written by Ivars Peterson for Muse magazine.

## August 24, 2007

### Changing the Soccer Ball

If you've kicked around a soccer ball, you've probably noticed the distinctive pattern on the ball's surface. For a long time, soccer balls have been stitched or glued together from 32 pieces of material. Twelve of these patches are five-sided (pentagons), and twenty of them are six-sided (hexagons). These patches are arranged so that each pentagon is surrounded by hexagons. Traditionally, the pentagons are colored black and the hexagons white.

This type of soccer ball is based on a geometric shape called a truncated icosahedron. An icosahedron has 20 flat faces, each one a triangle, with five triangles meeting at each corner. If you slice off the corner of an icosahedron, you reveal a pentagon. By slicing off all 12 of an icosahedron's corners, you end up with 12 pentagons and 20 hexagons. The new shape has 60 corners. A soccer ball differs from this shape in that its faces are curved rather than flat, which means the ball is just about as rounded as a sphere.

A truncated icosahedron (left) and a standard soccer ball (right). Wikipedia.

Now, there's a new ball design. It was introduced as the official soccer ball at last year's World Cup. Designed by engineers at Adidas, this ball is made from 14 curved panels to give it a smoother look and feel. It has fewer seams so the ball is rounder. Experts say the ball behaves more predictably that the old one did. You're less likely to get a wayward hook or an unexpected swerve when you kick it properly.

The official soccer ball for the 2006 World Cup is made from 14 curved panels. Adidas.

The official ball is also made from materials that make it practically waterproof. This makes a big difference when the ball gets wet. Because the old ball tended to absorb moisture and gain weight in the rain, it would fly slower, bounce lower, and curl less than the new one does.

Your soccer team is still probably using the old type of ball, but watch out for the new one. The way it bounces and bends might take you by surprise.

Muse, September 2007, p. 36.