The correlation between the hardness of a tennis ball and the distance it travels
Softer balls will be bouncier and thus, be able to travel longer distances as compared to harder balls.
When a ball hits the ground, the air inside the ball is compressed. Energy is stored in the compressed air and when the ball bounces upward, the compressed energy is released and the original condition of the air in the ball is restored.
A traveling ball will have both kinetic energy and potential energy. When a ball is lifted above the ground, it gains potential energy. When the ball is dropped and it begins to move downwards, the potential energy is converted to kinetic energy. As the ball touches the ground, the energy is temporarily stored in the compressed air inside the ball. As the ball rises upwards again the compressed energy is released and the ball gains kinetic energy. As the ball rises higher, the kinetic energy decreases and potential energy increases, causing it to fall down again.
As the ball continues to bounce, the height will reduce. This is because some of the energy that was stored in the ball is lost through friction between the air and the felt/rubber (surface) of the ball. This energy is lost and dissipated in the form of heat.
Be careful not to stand in the path of trajectory of the balls when they are launched.