What makes a ball bounce?
A ball bounces due to the pressure differential between the inside of the ball and the outside of the ball opposite to the point of impact. When a ball hits a hard surface, it momentarily deforms. This means that the inside of the ball now has less space to contain the air particles contained inside the ball. This compression increases the pressure inside the ball beyond the initial balancing pressure on the outside of the ball. This causes the ball to take off in the direction of the lower pressure. This is the same principle that makes a plane to take off. A hard surface creates more deformation at the point of contact. So, a ball bounces more off a hard surface compared to a soft surface.
The following three properties determine the performance and reaction of the ball to externally applied forces:
1. Ball size (circumference, radius, diameter): Typically, 27 to 28 inches
2. Ball weight (mass): Typically, 14 to 16 oz
3. Ball pressure: Typically, 8.8 to 16.2 pounds per inch
Page 65 of The Physics of Soccer presents a table of soccer ball sizes and specifications.
Science Tips for Players
Soccer players should be attentive to the following STEM factors that can, from a scientific standpoint, alter the state of play during a soccer game:
� Wind direction and speed as they affect ball movement
� Friction as it affects slippery playing surface and ball ground roll
� Humidity as it affects air moisture on and around the soccer ball
� Gravity as it affects downward motion of the ball
� Evaporation as it affects player comfort and health
� Force of collision as it may affect player motion and stability
� Ball inflation level as it affects bounce and mobility of the ball
