1.0 Introduction
Many sports played across the world that involves throwing, hitting and kicking are done so using a ball. However, many parameters such as humidity, materials of manufacture of the ball, size of the ball, etc. control the movement of the ball in air. Research on golf balls and tennis balls reveal their aerodynamic properties and the various parameters affecting their flight. The effect of seams on a baseball on the flight has been evaluated along with the relationship between rotation and lateral forces (Watts & Sawyer 1987). Similar studies have also been conducted on cricket balls, rugby balls, volleyballs etc. An important parameter that affects the physical and aerodynamic properties of a ball is the materials used in its fabrication. In this paper, the science behind choosing particular materials for manufacturing a soccer ball will be discussed with respect to how these materials affect different physical and aerodynamic parameters.
The different components of the soccer balls used in modern day football are
- The bladder
- The lining
- The stitching
- The outer cover
2.0 Description
There are numerous ways in which a soccer ball can be assembled. However, there one such design which is unique and stands out from among the rest. In this design, 32 polygons are stitched together, 12 of them five-sided and 20 of them six-sided, joined in a way that every pentagon is surrounded by hexagons. Traditional balls had the pentagons painted black and hexagons painted white. Many questions arise relating to the shape and design of the ball and this paper primarily focuses on answering a few of these questions. The maximum circumference allowed is 28 inches and not lower than 27 inches, while the weight of the ball at the start of the game must not be more than 16 oz. These rules are a part of the Laws of the Game book published by FIFA.
2.1 Soccer Ball Description and Specifications
A soccer ball consists of four primary layers: the bladder, lining layers around the bladder, stitching, and the outer most cover. The bladder defines the ball shape, while the layers of lining protect the bladder from stress incurred during play. The stitching keeps the ball together and is made up of special polyester materials. The cover material depends on the skill levels and the surface of play. However, the overall appeal of the ball depends on the cover where manufacturers stamp their company logos, or teams have their emblems embossed, etc.
The standard material used in fabricating a soccer ball is polyurethane stitched around a rubber bladder. Modern day soccer balls have a valve which allows inflation or deflation of this bladder. The synthetic panels are, usually, reinforced with polyester, held on by a suitable adhesive. The air pressure, according to the rule book, is not more than 15 pounds per square inch (psi) (Ken & Kerwin 2003).
2.2 The Individual Components
Even though the basic components of the soccer ball are the bladder and the outer covering, we can further breakdown these two components. While the bladder remains as it is, the outer covering consists of the inner lining to protect the bladder, stitching together the different panels of the ball and finally the outermost layer. We shall analyse these components individually.
2.2.1 The Bladder
The bladder is the innermost component of the soccer ball that defines the shape of the ball. When it is filled with air, it also determines the quality of kicks taken, as well its movement through air and subsequent aerodynamics. These bladders are either butyl or latex rubber. Butyl rubber retains air for longer durations and provides players with excellent contact quality. Even though this material is not as perfectly responsive as latex rubber, many butyl bladders are enhanced with 20% later for an improved feel. Latex, however, are preferred in professional games due to its soft touch and feel. Even though its air retention capacity is not as good as butyl bladders, it has better bounce and response. However, due to the presence of micro-sized pores on the surface, air escapes and makes it necessary to fill air on a regular basis. To overcome this issue, carbon in infused into latex that reduces these micro-pores.
2.2.2 The Lining
The lining of the soccer ball lies between the bladder and the outer cover. This is a crucial component of the ball that determines the durability and quality of the ball. Polyester reinforced synthetic leather is used to fabricate these linings. Lower quality balls have two layered linings while balls of better quality have four layers. They help in preserving the shape and structure of ball despite its rough use. It also protected the bladder from damage and deformation that is quite easily inflicted in soccer. To improve the feel and texture of these balls, an extra layer of foam is also sometimes incorporated.
2.2.3 The Outer Cover
The outer cover is made up of different durable materials and, usually, come printed with graphics, team or company logos, and colours that help spectators identify the ball during a game. Synthetic leather is the preferred material for manufacturing professional soccer balls. This material is more responsive and has a softer feel and touch while playing. However, this material absorbs moisture and becomes unsuitable to play during rains and snow and are not as durable as poly vinyl carbonate covered balls. To prevent deterioration and water absorption over time, these materials are reinforced with polyurethane plastics that also give it a glossy appearance. PVC, on the other hand is more reliable and durable and suited for long term use.
3. The Soccer Ball Assembly
All the panels, the lining materials, and the bladder are packed together in a kit for the tailor or the stitcher. Starting from one panel, the stitcher assembles and stiches all the panels together in a proper order. Before stitching, it is important to understand the effects the number of panels has on the performance of the soccer ball. For instance, even though traditional balls have 32 panels stitched together, fewer panels between 6 and 26 provide better aerodynamics and can also deliver higher air speeds and curvature through the air. However, more panels provide better control and structural stability.
Once the number of panels is determined these panels are stitched together using 5-ply polyester that are usually reinforced with Kevlar. The stitching can either be by hand which result in balls that have strong seams and highly improved performances. Hand stitched balls also have longer durability. Machine stitched balls are not as durable, but are less expensive than the hand stitched balls. However, the balls that are used in professional matched have thermally bonded seams where panels are thermally fused together. This kind of stitching provides the ball with optimal flight and performance (LaBlanc & Henshaw 1994).
4. Soccer Balls in Play
The soccer ball needs to inflated and ensured that sufficient air has been filled in the bladder before kick-off. The air pressure needs to be maintained under the prescribed limits. The referees need to ensure that the ball’s dimensions and weight and the different parameters are within the rules mentioned in the FIFA rulebook. Once this is done, the ball is ready for play. When the referee blows the whistle the ball is kicked into motion by a player from a team selected by the toss of a coin. The ball is either kicked or headed from one player to another until a player shoots the ball past a goalkeeper to score a goal.
5. Conclusions
Many premier soccer ball manufacturing companies have come up with superior materials and designs that greatly improve the quality of the game. The ideal soccer ball is waterproof, flight accurate with pinpoint precision, higher air velocities, and is able to completely absorb all the momentum transferred to it during a kick. Besides the geodesic design conventional soccer balls possess, different physical and aerodynamic properties depend on a number of other factors such as materials used in manufacture, air pressure, compressibility, etc. The trick lies in optimizing the shape of the ball with all these parameters to obtain a ball that is suitable for a World Cup game!
More information on the soccer ball can be found from the following sources: Watts & Sawyer in “Aerodynamics of a knuckleball” discuss in detail the aerodynamics of different balls among which they have mentioned the soccer ball as well. This paper is accessible from the American journal of Physics published in 1975. David Goldblatt gives a comprehensive history of the evolution of the soccer and how the soccer ball evolved through the years in “The Ball Is Round: A Global History Of Soccer” published by Penguin. This book is available on most e-commerce portals and can also be accessed through different institute libraries. However, for an easier access to understanding the composition of the soccer ball, numerous online sites are available that freely discuss the soccer ball composition with the help of credible sources. One such website is provided in the reference section.
References
Watts, Robert G., and Eric Sawyer. "Aerodynamics of a knuckleball." American Journal of Physics 43.11 (1975): 960-963.
Goldblatt, David. The ball is round: A global history of soccer. Penguin, 2008.
Bray, Ken, and David Kerwin. "Modelling the flight of a soccer ball in a direct free kick." Journal of sports sciences 21.2 (2003): 75-85.
“Welcome to Kicker Sports Welcome to Kicker Sports Kicker Sports, n.d. Web. 05 Dec. 2014. <http://www.kickersports.com/support.php?mID=117&sID=0&Page=1&PageName=Components-of-a-Soccer-Ball>.
LaBlanc, Michael L., and Richard Henshaw. The World Encyclopedia of Soccer. Gale Research, 1994.
