Originally Posted by bhupaes
No, I didn't confuse anything. If one were only depending on centripetal force, any muscle not used for gripping the racquet will be passive. Try swinging like that and see where the ball goes.
I will stick with everything I've said in this thread - let's just agree to disagree.
It is not just centripetal force, there is also linear acceleration that has to be supplied, the path is not perfectly circular, gravity is involved, etc. Obviously twirling a stone on a string is not like hitting the tennis ball. For example, I have explained many times why the two-pendulum model of passive swing is wrong and led to wrong calculations.