Even amateur adult players can boom a soccer ball 50 yards or more down the field, from the goal area past the halfway line, and professional goalkeepers such as Manchester United's Edwin van der Sar can make the ball sail three-quarters of the length of the pitch. A distance kick requires the ball pumped up to be acceptably hard, which the referee tests before the game by pressing his palms on either side of the ball just before kickoff. Engineers and sports scientists -- as well as science fair participants -- have devoted attention to learning how the air pressure affects the distance a soccer ball goes when kicked.
FIFA, the international governing body of soccer, requires adult players to use a ball between 27 and 28 inches around, between 14 and 16 oz. in weight, and pressurized to the equivalent of 0.6 to 1.1 atmospheres, which translates to 8.5 to 15.6 pounds per square inch. A ball pressure gauge, with a needle that goes in the soccer ball valve and a dial measuring up to 20 psi, can tell precisely if the ball is within the mandated range. A cheaper practice ball may be labeled to be inflated within the range of 6 to 8 psi; in this case the referee will decide by feeling the ball whether to stay within the manufacturer’s recommendation or increase the pressure to the minimum of 8.5 psi, notes the U.S. Soccer Federation on the website Ask a Soccer Referee.com.
The higher the air pressure inside the soccer ball, the farther it will go when it is kicked, writes engineer and soccer ball enthusiast Bruce Rigsby on the site Soccer Ball World.com. Your kick transfers more energy to a stiff ball, compared to a spongy one, as less of the energy is lost to deformation of the ball’s surface. Thus, the extent of air pressure in the ball affects how far it sails off your foot. The same concept applies with other inflated sports equipment: A basketball bounces lower if not inflated properly, and a bicycle tire contacts more of the road if underinflated, reducing performance.
Atmospheric air pressure also affects the distance the ball travels when kicked, Rigsby states. The lower the pressure, the less friction. A ball kicked at altitude in Mexico City, for example, travels further than a ball kicked at sea level in Miami Beach. This is the same principal that leads to so many home runs being hit at the Colorado Rockies’ home, Coors Field, a mile above sea level, as a baseball also travels with less friction at altitude.
The principles of how air pressure affects a kicked soccer ball travel make the topic suitable for testing as part of a science fair project. Science educator and author Muriel Gerhard of Education.com recommends inflating a soccer ball at low, medium and high levels and kicking the ball at the same force inside a gym. Have a helper mark the spot where the ball lands each time. Perform three tests at each pressure, record the results and average them. Create a line graph of the data, and report on your initial hypothesis and how the results bore them out.