![[IOP]](http://images.iop.org/cws/icons/themes/phw/colophon-small.png){kind=icon}
By James Dacey
In three days’ time all eyes will turn to South Africa as the first match kicks off in the 2010 FIFA World Cup, the first time the tournament has been hosted by an African nation.
Love it or loathe it, football has developed into a truly global force where fans are now interested in many different aspects of the game from the silky skills of the top players to the fashion styles of the wives and girlfriends.
One aspect that hasn’t changed over the years is the underlying physics of the game, notably the aerodynamics that governs the behaviour of the ball. Indeed back in 1998 we published a feature about this topic inspired in part by a freakish goal by the Brazilian fullback, Roberto Carlos, which appeared to defy the laws of physics.
Playing in a tournament in France, Carlos struck a free kick 30 m from his opponents’ goal. It was heading so far wide of the goal it made a ball boy, standing several metres to the right of the goal, duck his head in response. Then, once the ball had cleared the wall of defenders, it took a wicked late swerve into the top right hand side of the goal, leaving the crowd and subsequent viewers truly gobsmacked.
After scoring that spectacular goal, Carlos took every opportunity to try to repeat the trick but never quite managed it.
The Physics World feature, co-authored by sports engineer Steve Haake of Sheffield Hallam University, breaks down this legendary strike to explain the aerodynamics of the ball’s flight. It confirms something that I have suspected for a long time: that Carlos is not actually a magical free-kick taker, but that some highly unusual atmospheric conditions were in play that memorable night in Paris.
It is a fascinating read and the article also looks more generally at the aerodynamics of sports balls and the kind of research that can explore these processes.
After teaching projectile motion, I use the following simple exercise to motivate students to play football. Background: This topic includes two equations, one for the time of flight, T, and other for the range of projectile, R. Both equations are based on i) initial velocity, ii) the angle of launching of projectile and iii) the acceleration due to gravity, g, – assuming the air resistance to be negligible. Here, the initial velocity and angle of launching have to be measured, using the photographic technique but T and R can be easily measured by students on the ground. Therefore a teacher can ask students to derive an equation for either initial velocity or angle of launching, based on R, T and g only. The equation for angle of launching (theta) is: tan(theta) = (gT^2)/2R. They become very happy after deriving the fore-going equation because it is not found in the texts usually.