It's World Cup time and that means sports fans worldwide are focused on important issues, like complaining about vuvuzelas and this year's soccer ball, the Jabulani, which will push fan and player hatred of the 2006 ball, Teamgeist, into the background.
Why does this happen (the ball complaints, not the vuvuzelas) every World Cup? FIFA, governing body of Big Football, loves controversy, that's why. So FIFA has strict regulations on the size and weight of the balls but makes no regulations at all about the outside surface of the balls. Thus, we go from an inordinately smooth ball one World Cup to one with ridges the next.
"The Teamgeist was a big departure at the last World Cup. Because it was very smooth – much smoother than a regular soccer ball," says Professor Derek Leinweber, Head of the School of Chemistry&Physics at the University of Adelaide, "it had a tendency to bend more than the conventional ball and drop more suddenly at the end of its trajectory. By comparison, the aerodynamic ridges on the Jabulani are likely to create enough turbulence around the ball to sustain its flight longer, and be a faster, harder ball in play."
John Eric Goff, associate professor of physics at Lynchburg College in Lynchburg, Virginia, goes into more detail in this month's Physics World, outlining how the Jabulani's surface roughness and asymmetric air forces contribute to its path once it leaves a player's foot. He also says the reduced air density in games played at higher altitudes, like those in South Africa, can contribute to some of the reality-bending ball trajectories already seen in some of this tournament's matches.
Gotta love unpredictability. We have the lowest scoring World Cup in history but some of the goals that have hit home looked like physics miracles rather than science. Obviously the underlying physics is the same, players are just not adjusting as they had to previous competition balls.
As we have discussed many times in the past regarding baseball and other sports, the Reynolds number of the air, Re = VD/ν - where V is the ball’s center-of-mass speed relative to the air and D the ball’s diameter, while the kinematic viscosity ν is the ratio of air’s viscosity to its density ρ - is vital to understanding how a soccer ball will move.
Those viscous interactions with the ball give rise to the drag force, which points opposite to the ball’s velocity. Goff describes that drag force as FD = (ρV2/2)·A·CD ( the extra A you now see being the ball’s cross-sectional area and CD the dimensionless drag coefficient) and when there is a drop in CD there is a drag crisis, which indicates the transition from laminar to turbulent flow - about 12 m/s, he says, comparable to that of a medium-range pass.
Goff says they used wind tunnels and numerical models to study the traditional 32-panel soccer ball and the Adidas Teamgeist ball from 2006, with its 14 thermally bonded panels, and they failed to find any significant differences in CD over a wide range of Re, but they do suggest that the Magnus force on the Teamgeist ball is slightly larger than on the 32-panel ball.
When will they get a 2010 Jabulani ball? Soon, we have to hope. We are sure the Brazil team will be happy to send him one of they lose in the final match.
See also: J. E. Goff, M. J. Carré, “Soccer Ball Lift Coefficients via Trajectory Analysis,” Eur. J. Phys. 31, 775 (2010)
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- Kudos To "The Independent" Newspaper For Debunking Nibiru "Blood Moon" Hoax
- Climate Change Has Less Impact On Drought Than Previously Expected
- Dogs Understand Both Vocabulary And Intonation Of Human Speech
- Your Microbiome Did Not Cause Your Weight Problem
- Fewer Cardiovascular Drugs Being Studied In Clinical Trials
- State Of Academic Freedom 2016
- USDA Microbiologist Warns Bacteria In Vaping Products May Be A Health Concern
- "Apparently planet 9 exists. Not Nobiru but another dwarf planet. This planet could destroy a couple..."
- "Thank you. You know, I am of the firm belief that if a blog has a title that includes Science in..."
- "Firstly, I want to inform everyone apart from Kaylee that the following doesn't apply to the topic..."
- "Hello again Robert, Once again, thank you for your informative reply. It's wonderful to still find..."
- "Hi Margaret, thanks, glad you like my replay, and any views are welcome here :). It's only trolling..."
- <a href="/news/2016/08/29/how-herpes-drugs-work-9926">How Do Herpes Drugs Work? <i class="fa fa-angle-double-right"></i></a>
- <a href="/news/2016/08/30/school-meals-eat-tu-principals-9938">School meals - Eat tu Principals? <i class="fa fa-angle-double-right"></i></a>
- <a href="/annual-reports">Annual Reports <i class="fa fa-angle-double-right"></i></a>
- <a href="/news/2016/08/30/some-sugars-help-babies-thrive-9934">Some Sugars Help Babies Thrive <i class="fa fa-angle-double-right"></i></a>
- <a href="/news/2016/08/30/concussion-recovery-time-cut-half-when-athletes-immediately-sit-9933">Concussion Recovery Time Cut in Half When Athletes Immediately Sit <i class="fa fa-angle-double-right"></i></a>
- <a href="/news/2016/08/29/icymi-acshs-most-popular-articles-summer-9931">ICYMI: ACSH's Most Popular Articles of the Summer <i class="fa fa-angle-double-right"></i></a>
- Progress in refining the genetic causes of schizophrenia
- Researchers discover machines can learn by simply observing
- Technique could assess historic changes to Antarctic sea ice and glaciers
- Factors associated with improvement in survival following heart attack
- System may help treat rare genetic disorder, reduce severe side effects