Posted by: Mike Myers (mike.myers@bell.ca) on Fri Sep 30 11:18:53 2005

> > > IMO, the only reason the coefficient of friction of the hitting surface would make a difference is because you are thinking the way to generate rotation is to push with the rear leg and block with the front leg. I think this is a "way" to generate rotation, but certainly not the optimal way. One might even think that this is the way MLB players generate roation by watching their clips. Front leg does "appear" to firm up, etc. But what is actaully happening is a "result" of the body fully unloading and completing rotation. Optimal rotation should start in with the body's core muscles(pelvic, abdominal, upper thighs) and generate down through the feet and out through the shouldersarms. Body weight has little if anything to do with producing force in the rotational swing. It's all about loading/unloading those core muscles.
> > >
> > > > Jack,
> > > >
> > > > People have problems adapting cage work to game situations for several reasons. Lack of live pitching experience is generally cited as the reason for poor transfer of mechanics between environments.
> > > >
> > > > How important is body weight, however? It occurs to me that even if one were perfectly able to hit live pitches in a cage (or by addressing a heavy bag, and graduating to soft-toss as you suggest), a huge difference from game situation is typically the ground co-efficient of friction (solid floor, to typical batter's box sand, for example).
> > > >
> > > > Have you found a weight "floor", such that if a batter weighs less than this, he can never drive the legs without significant foot slipping (regardless of body strength) and develop great power.
> > > >
> > > > Since frictional force is represented as a fraction of the normal force (fractional coefficient depending on surface type), it seems even a very strong batter will be ineffective if he cannot produce a large normal (i.e. body weight) force to drive rotation.
> > > >
> > > > Regards,
> > > > Mike.
> >
> > Jeff,
> >
> > Regardless of where in the body forces are initiated, the ground must be used to drive rotation. If the upper body swings in one direction, the lower body wll react in the opposite direction. The only thing which prevents feet from rotating in opposite direction of arms is ground friction.
> >
> > Do you believe one could could swing equally well standing on a smooth ice surface?
> >
> > Mike.
>
>
>
> I do agree that it would be harder to hit a ball on ice, but it has nothing to do with body weight(which is what you were suggesting). It would be just as hard for a 400 lb. person to do it as it would for a 100 lb. person. I disagree also that the ground(or body weight for that matter) "drives" rotation. The feet are just attached to the ground to keep the axis of rotation stationary. The core muscles of the body drive rotation. And I certainly wouldn't agree that the feet would want to rotate in opposite direction of the arms. Once rotation is initiated, the entire body will want to rotate in the same direction. Are you saying that if your body is rotating in a counter-clockwise direction(as a right handed hitter), that your feet would want to rotate in a clockwise direction if they weren't attached to the ground? Seems like that would either stop the rotation completely, or twist yourself in a knot.

Jeff,

"I do agree that it would be harder to hit a ball on ice, but it has nothing to do with body weight(which is what you were suggesting). It would be just as hard for a 400 lb. person to do it as it would for a 100 lb. person."

No. Ice is a surface with a defined co-efficient of friction:

http://hypertextbook.com/facts/2004/GennaAbleman.shtml

The force of friction on ice = (ice co-efficient) x (Normal force)

The normal force is weight of the batter, so the force of friction is directly proportional to the batter's weight. A batter can supply a drive force equal to his frictional force limitation. If he supplies any more than this, however, he will slip. Thus, a heavier batter has a higher frictional force limitation, and can supply more drive force before slipping.

"Are you saying that if your body is rotating in a counter-clockwise direction (as a right handed hitter), that your feet would want to rotate in a clockwise direction if they weren't attached to the ground."

Yes - this is just an application of Newton's 3rd Law: force of A on B = force of B on A:

http://theory.uwinnipeg.ca/physics/force/node4.html

Try sitting in a swivel chair with your legs raised. Now swing your arms in one direction as if batting - see which way the chair rotates.

"Seems like that would either stop the rotation completely, or twist yourself in a knot"

Precisely why the ground is a factor. The more slippery the surface (i.e. lower co-efficient of friction), the more your feet are permitted to counter-rotate on the ground. A good ground surface provides high resistance (i.e. coefficient of friction) so that you can ultimately push off and move the entire body in one direction.

Regards,
Mike.