The host nation for the 2022 World Cup will be Qatar, a desert country where temperatures in June and July can reach 50 °C. I find it hard to even imagine that level of heat, let alone play football in it! The extreme temperatures are of obvious concern. So, alternative measures are being considered to ensure games at this tournament are not played at extremely high temperatures. These include playing in the winter or more likely building climate controlled stadiums. At present it looks as though 5 brand new climate controlled stadiums will be built. The primary concern is the detrimental affect of extreme heat on human performance. To a lesser extent, temperature is also likely to effect the physical properties of the ball, changing the speed a player can kick it. This blog will explain the effect of temperature on soccer ball dynamics.
Spherical sports balls, such as baseballs, golf balls, tennis balls, squash balls and footballs, are made from viscoelastic materials. The mechanical properties of these materials are dependent on both the rate at which they are deformed (i.e. how fast they are struck) and the temperature at which they are deformed. In this instance we are interested in the effect of temperature. Sports engineers often determine the performance of sports balls by firing them against a rigid surface and measuring the response with a high-speed camera. Published studies have shown that for constant impact speed the rebound speed of tennis balls, squash balls and baseballs all increase with temperature.
Effect of temperature on soccer balls
We were interested in determining the effect of temperature on soccer ball dynamics. So, one of our Sports Engineering MSc students, Nicki Wiart, undertook her project on this very subject in collaboration with adidas. Nicki measured the effect of temperature on the ball’s materials in addition to its impact properties obtained from firing different temperature balls against a rigid surface. In summary, the stiffness of the material decreased as temperature increased, while the rebound speed of the ball increased. The results were applied to a typical penalty kick scenario by using a simple effective striking mass model combined with a trajectory model. The results showed that the time available to the goalkeeper was 7 per cent shorter at 40 °C in comparison to that at 0 °C (See figure below). Therefore, the time available for a goalkeeper to prevent a goal decreases as temperature increases. For those who would like more details the journal paper which came out of Nicki’s MSc project can be found here.
Air conditioned stadiums are likely to be used at the 2022 World Cup. If this is the case, game temperatures will be virtually constant and the properties of the ball will not change. However, the balls may be used outside of the air-conditioned stadiums, in training for example, where it will be hotter (even in the evenings). Assuming the tournament ball is constructed from similar materials to the one we tested the players will probably detect slower ball speeds within match play. Therefore, attempts are likely to be made by ball manufacturers, such as adidas, to limit the influence of temperature. A possible solution would be to manufacture a ball from materials which have constant (or as close as feasibly possibly) properties from around 0 to 50 °C.