Science of the World Cup football

Materials World magazine
,
4 Aug 2014
The Brazuka ball. Copyright Adidas

The standard of this year’s FIFA World Cup was up there with the best of them, and some credit must go to the ball itself. What was the science behind the Brazuca football? Simon Frost finds out.

What’s the background?
Adidas has provided every World Cup ball since 1970, but the 2014 ball needed to be something extra special, after players variously described 2010’s Jabulani model as ‘unpredictable’, ‘like a beach ball’ and ‘a catastrophe’. Cue the Brazuca, which was developed by Adidas and German company Bayer MaterialScience.

What about the design?
The main innovation of the Brazuca is its outer surface, which comprises six propeller-shaped polyurethane panels, each spotted with many tiny dimples, reducing drag in the same way as a golf ball. The seams of the thermally bonded panels are 1.56mm deep – more than three times deeper than those of the Jabulani – and are also longer. All of these features create a rough surface, which increases friction between foot and ball for improved control but, most importantly, increases spin, reducing the occurrence of the knuckling effect. NASA’s aerodynamics researchers explain this effect as when ‘at zero or near-zero spin, the seams of the ball channel airflow in an unusual and erratic manner, making its trajectory unpredictable’. Traditionally, balls knuckle at around 48kph, which is slower than the average shot, so some skill is required to use it to a striker’s advantage. The much smoother Jabulani knuckled at more common striking speeds of 80100kph, so the effect occurred frequently – and not always intentionally.

What other materials were used?
From the inside out – the bladder is made of butyl rubber, surrounded by four layers of polyamide – a thin fibre-reinforced composite layer, followed by a thicker open-cell foam layer, another thin fibrereinforced composite layer, and a final closed-cell foam layer. The foam provides softness under compression when the ball is struck, while the fibre-reinforced layers help to spring the ball quickly back into shape afterwards. These reinforced layers also take the brunt of the pressure to maintain the flexibility of the foam.