A ball is rotating with the constant angular velocity at one end of a perfect string that is tightly tied (assume fixed) to a wooden bar at the other end. Its tangential velocity is as follows:

Concept: The motion will force the string to wrap itself around the wooden bar because the other end of the string is attached to it.

As a result, the effective radius of the circular motion will be reduced. 

Tangential velocity v = ωr, the tangential velocity will decrease with time.