[ThinkingPlus]

What is it? How does it function in a golf swing? Is it useful for both methods of accelerating the club (hitting and swinging)?

I think this is an important topic . . . but I'm not really qualified to discuss the physics aspect because of the genetic crap shoot and all.

Well, here is what happens when clubhead meets ball. This may not mean much relative to swing, but it will give everyone something to start with.

Mball * Vball_after + Mclub * Vclub_after = Mclub * Vclub_before (the before and after refer to impact)

Basically, since this is an elastic collision, momentum is not strictly conserved, but it is close enough for our purposes. You can also approximate Mclub with the mass of the clubhead alone since the impact interaction occurs over such a short time.