Roll-a -ball tutorial ball can't be rolled

I did everything correct while watching tutorial videos. However, I just couldn’t roll the ball. Even I hit the play button, the ball was still and nothing happened. I wonder what’s wrong with it and what should I do to roll the ball. Thank you. There are the script and interface…

I think to remember that you have to drop the sphere from above (0.5 or so) otherwise it doesn´t start to roll?