FIX

[ThinkingPlus]

There are quite a few resources on the web which indicate that the golf ball is in contact with the golf club when hitting a driver (~ 100 MPH) for ~ 500 microsec (1e10-6). Given that information, one can calculate the distance the club travels with the ball in contact assuming constant velocity (keeping it simple).

100 MPH => 100 * (5280 ft / 3600 sec) * (12 in. / ft.) * 2.54 cm/in
= ~4500 cm/sec * 500e-6 = 2.25 cm ~ 0.89 in.

I don't know if this is all that useful or not. It would be better to have impact time vs. clubhead speed for a given ball type, but I have never seen that depedency measured or calculated. It would be easy enough to do with a high speed (very) camera and a repeatable club swinging device. Oh, well. Enough physics / math stuff. Back to work doing more physics / math stuff

[Mike O]

Thanks for the feedback- but I think - and you may already have implied- that we're really looking for something that shows the center of gravity of the ball or center of the ball- moving while the ball is on the clubface. Certainly the contact time period from impact to separation may not include any movement of the center of the ball.

[ThinkingPlus]

I would expect that if the club face moves a little over 2 cm while in contact with the ball, then the center of the ball moves that much as well. Think of it this way. At initial contact, the center of the ball is 1/2 ball diameter from the club face. At the end of the contact period, ~ 500e-6 seconds later, the center of the ball is once again (approximately) 1/2 ball diameter from the club face. However, in the intervening time the club face has translated along the swing path ~ 2 cm. Therefore during that same time, the center of the ball has translated the same 2 cm.

I have not looked into this sort of thing in that much detail, but to first order my description above seems reasonable. It also may not be entirely pertinent to your discussion.

[Yoda]

Per 2-D-0:

"The force of the Impact will hold the ball against the face of the orbiting Clubhead and so carry it along the same circular path. "

[tongzilla]

Thanks Yoda for the useful quote. So (to answer Mike O's question) the center of gravity of the ball does move during impact interval?

If that's true, then according to Mike, there's a contradiction in TGM. But I think this hook-face thing Homer talks about on page 24, which diverts the ball from it's true tangential path, should save the day...2-D-0 has always been foggy to me.