Sorry for the link, but this is my old question http://answers.unity3d.com/questions/1407546/problem-with-a-ball-to-roll.html and nobody answer it, but maybe this time somebody can help me with this problem. All scripts and informations in the link, please if anybody know how to solve my problem tell me that.
there is an answer in your old question. I did it with add Physic-> Rigidbody to the ball.
Does this help?