Soccer balls come in different sizes and weights. Further details can be found at Philip Vasan, an internet resource. A soccer ball weighs 396-453 grams and is inflated with a pressure of 1 kg per square cm or atmosphere at sea level. 70 Before the ball was leather and could absorb considerable amounts of water when it was used in wet fields. In the mid-70 was amended to invest it with a waterproof material but it could still gain mass to retain water. The ball now is synthetic and resistant to water absorption. In interpreting the literature is important to pay attention to the probable date on which the players performed to take into account if they used leather ball. In sports media notes mention that kicked the ball travels at a speed greatly increased to 100 km / h. But players rarely voluntarily nod the ball thrown at that speed although accidental impacts are possible from the head.
The ball More nod voluntarily fast a player is at a speed of 70-85 km / h suggests that most of the time the pitch occurs at speeds below 65 km / h head hits the ball with less force than a typical punch in boxing producing an acceleration of the head of 20g to 100g of a punch. It is estimated that a player heads the ball 5-7 times during a game and 9-10 times in training.