it's a circle...
The tennis ball is distorted from its round shape when it hits the ground, which means the volume inside is reduced or the air inside is being compressed. The air then pushes back to restore the tennis ball's original shape and therefore bounces off the ground.
Shape Or Mass
Maybe different color, shape, substance, or weight.
If the ball has a dent in it and you heat the ball in hot water it will come back to its original shape.
A tennis ball.
a golf ball weighs more than a tennis ball
so it has a large surface area and is easier to hit the Ball with
a tennis ball