Futbol Topunun İngilizce Tanıtımı

Futbol Topunun Özellikleri İngilizce Makale

The Soccer Ball The soccer ball is characterized by its mass, diameter, internal pressure and surface texture. The full size ball is required to have a mass between 396 g and 453 g, a circumference between 68.5 cm and 71.1 cm, and an internal pressure of 0.6 to 1.1 atmospheres. The outer casing or cover should be of leather or another approved material which does not prove dangerous to players. It may be constructed in two main ways either with panels of material sewn together, or moulded from rubber or plastic with cover panels bonded or painted to the surface. The mass of the ball is restricted by the rules of the game but small variations in mass can occur due to the absorption of water through the seams of the ball, or by absorption through the material. It has been found that both moulded and stitched balls absorbed moisture after a prolonged period of soaking, and that the moulded ball increased its mass by 1.3 % while the stitched ball increased its mass by 7.5 %. The increase in mass yielded an increase in impact force of 2.8 % for the moulded ball and 8.5 % for the stitched ball. The increase in force was thought to be directly related to the increase in ball mass (Armstrong et al. 1988). In comparison of the impact force for moulded and stitched balls dropped from 18 m (providing an impact velocity of 18 m/s ) was found that the mean impact forces ranged from 851 N for the moulded ball to 912 N for the stitched ball and the rise time of the moulded ball was 27% lower than for the stitched ball (Lewendusky et al. 1988). The performance of a ball is described by the way it flies through the air, bounces, slides and rolls on the ground. It is known from mechanical theory that a heavier ball will retain more of its initial velocity during flight, and that the aerodynamic forces of drag and lift acting on the ball will cause it to alter its flight path, particularly when the ball spins. Spin affects ball flight markedly, to the extent that the use of ball spin becomes a game tactic and as such, one might expect that characteristics of ball construction on this aspect of performance would have been scientifically investigated. There is published research on the flight characteristics of the soccer ball as a function of ball variables including spin. If the release angle, release velocity and spin have been constant, the projectile of the ball has been more stable than with the without spin (Luhtanen et al. 1993). When dropping a soccer ball from a height of 18 m and hitting the target force platform below. The success rate hitting the target was no better than 7% (Lewendusky et al. 1988). This was explained by the aerodynamic Magnus force acting on the ball as it slowly rotated during its descent. With regard to bouncing, sliding and rolling it has been shown that the resilience of the ball on the surface is determined more by the characteristics of the surface than the ball. This is also likely to be true of the frictional properties between a ball and the surface which determine its skid and roll behavior.