Brazuca over Jabulani for better football, say physicists

Say hello to Brazuca, the official football of the 2014 FIFA World Cup. Brazuca is a ball designed and produced by sportswear manufacturer Adidas, which also produced the Jabulani used in the 2010 World Cup. Both balls are part of a legacy where designers are reducing the number of panels they are constituted by. Until the late 2000s, the conventional football had 32 panels of hexagonal and pentagonal shapes. Jabulani has eight panels and Brazuca, six.

However, that didn’t do much good for Jabulani, which faced a lot of flak during the 2010 FIFA World Cup, for which it was made, because of its wobbly movement through the air. And according to a study in Scientific Reports published May 29, scientists have figured out why and found the problem fixed in Brazuca.

Sungchan Hong and Takeshi Asai, both from the University of Tsukuba’s Institute of Health and Sports Science, used a wind-tunnel and a robot to kick balls toward goal-posts 25 m away, to study the spheres’ non-spin aerodynamics. Their results show that Brazuca displayed very little of the irregular fluctuations that Jabulani did, and other improvements besides, because of the shape of its panels and their rough surface.

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Photograph of the wind tunnel test setup. Image: doi:10.1038/srep05068
Photograph of the wind tunnel test setup. Image: doi:10.1038/srep05068
Photograph of the wind tunnel test setup. Image: doi:10.1038/srep05068

When a smooth, spherical ball with seams is kicked up, streams of air moving near the seams exert a different amount of force on the ball than air flowing around elsewhere. This asymmetry gives rise to a wobbly movement of the ball, which Jabulani was especially susceptible to. At the time, it was considered to be one of the reasons the tournament’s first leg had as few goals as it did. Rabindra Mehta, Chief Aerospace Engineer at NASA Ames Research Centre, told Discovery, “You want to see more consistent, rounder balls that are totally water-proof. That’s all good stuff, but perhaps the aerodynamics was not looked at as carefully as [Adidas] should have.”

Jabulani also fell behind because, according to Hong and Asai, the asymmetry of forces was influenced by how the ball was oriented, too. Specifically, “the amplitude of the unsteady aerodynamic forces acting on soccer balls changes according to the number of panels as well as the directions they are facing,” they write in their paper. This means Jabulani moved differently depending on how it was facing when kicked.

Amplitude with respect to unsteady aerodynamic forces (blue line: side force, red line: lift force) of soccer balls derived using fast Fourier transform at flow speed of 30 m·s−1.
Amplitude with respect to unsteady aerodynamic forces (blue line: side force, red line: lift force) of soccer balls derived using fast Fourier transform at flow speed of 30 m·s−1. (a, b) Brazuca, (c, d) Cafusa, (e, f) Jabulani, (g, h) Teamgeist 2, and (i, j) conventional ball. From: doi:10.1038/srep05068

Hong and Asai also observed that there was a marked difference in the asymmetry of forces on Jabulani and Brazuca at higher speeds, such as during a freekick (30 m/s), with Jabulani consistently out-wobbling the others.

Brazuca overcomes these issues by boasting a rough, nubby surface. It reduces the asymmetry of air-flow and makes the ball’s motion smoother through the air. Second, the arrangement of Brazuca’s six curvaceous panels ensure the ball moves the same way no matter how it is kicked. With respect to the other balls, Hong and Asai write, “Brazuca and the conventional ball exhibited relatively stable and regular flight trajectories compared to Cafusa, Teamgeist 2, and Jabulani, whose panel shapes varied significantly with the orientation and were characterized by relatively irregular flight trajectories.”

However, this stamp of approval doesn’t count for much because conditions on a football field in Brazil are going to be very different from a controlled environment in a lab in Japan. There’s going to be wind, more or less humidity, different temperatures, the ball’s attitude during rains, etc. – not to mention players’ level of comfort. These are the real deciders, and only time will tell if Brazuca is in every way better than Jabulani.

But as far as the physics is concerned, Brazuca should make for better football.


Featured image: Adidas Brazuca, ИЛЬЯ ХОХЛОВ/Wikimedia Commons