Conceptual question about torque and balls

[Niles]

[SOLVED] Conceptual question about torque and balls

Homework Statement

Take a look at the following thread:

https://www.physicsforums.com/showthread.php?t=147053

In this thread, the torque is measured from the center of the ball. Can I measure it from the point where the ball and the ground touch each other, so the torque is:

T = mgsin(a)*R = I*alfa?

I tried, and it gives me that a = (3/2)gsin(a), which is wrong - why?

 

[Niles]

No, then again I get (2/3) rather than (3/2) - but still it doesn't work.

 

[Niles]

Any suggestions? I would really like to know, whether am I wrong or right about this.

 

[Niles]

No suggestions at all :)?