... powered by rotating the wrist. The faster we rotate the ball, the stronger the dynamic and torsion is produced. The speed ... RPM.Function:1.Perfect exercise gadget for sports like golf, tennis, squash, cricket, badminton, baseball, bowling, basket-ball,, motocross, mountain climbing.2 ... of silicone rubber on the surface of the ball. That can prevent the ball from sliding down to the ground, and the ...