KENKO BALLS (Made in Japan)
Kenko balls are soft, hollow, rubber balls used as official youth balls for baseball and softball in many countries around the world. The one in the photo is a ̉CÓ ball, weighing 129 g and has a wall thickness of 8 mm (4 mm of white rubber plus 4 mm of black rubber – hard to see in the half ball photo unless you move your head around to view from a different angle). Force vs time curves are shown when each ball is dropped 10 cm onto a hard surface. Impact duration increases with ball mass and decreases as ball stiffness increases. Impact force increases with both ball mass and ball stiffness (and also with ball speed).