|Tipler, Paul A. College Physics. USA: Worth Incorporated, 1987: 169.||"A soccer ball of mass 0.43 kg leaves the foot of the kicker with an initial speed of 25 m/s."||430 g|
|"Soccer." Encyclopedia Americana. 25th ed. Connecticut: Grolier Incorporated, 2001.||"It must be 27 to 28 inches (69-71 cm) in circumference and weigh between 14 to 16 ounces (394-454 g)"||396–454 g|
|"Official Rules of Soccer."Chicago: Triumph Books, 1997.||"The weight of the ball at the start of the game shall not be more than 450 g nor less than 410 g."||410–450 g|
|Hockok, Ralph. "Soccer." New Encyclopedia of Sports. USA: McGraw-Hill Book Company,1977.||"Its weight at the brginning of the game is 14 to 18 oz, and the inflation pressure is 12 to 13 lb."||400–510 g|
|Harris, Paul. Spalding Soccer Handbook. USA: Masters P, 1992.||"The ball must be made of leather or have a leather-like cover and be 27-28 inches in circumference, weight 14-16 ounces and have 14 pounds of air pressure. (Youth leagues may use smaller balls.)"||400–450 g|
Soccer was originally called "association football,"but the existence of the game of American football made differentiation between the sports difficult. Therefore, the term "association football"became known as the word soccer, which is derived from the word assoc. It is the most widely played team game and the most popular spectator sport. It is played by two teams each consisting of 11 men on a rectangular field (110 m x 73 m) having a goal of 7 m wide and 2 m high at either end. At the start of a soccer game, the soccer ball, a spherical leather football, is 27 to 28 inches (69-71 cm) in circumference and 14 to 16 ounces (396-454 grams) in mass. The goalkeeper is the only player that is allowed to handle the ball. The remaining players are permitted kick, dribble, and pass the ball with their feet, head, and trunk. A goal is scored when the ball is sent between the opponent's goalposts.
Louise Huang -- 2002