Posted by: JJA () on Wed Nov 3 12:39:51 2004

>>> Jack,
>
> I agree with your demonstration on the video. If you just thrust the knob of the bat at the ball, of course you don't get the whip effect. There is no disagreement with us there.
>
> Rotation is 100% important to make the whip effect work! As I've said before, I think of the wrist joint as a joint that is free to move. When the lower body and torso rotates, the arms and bat are rotating as well. As the bat approaches the hitting zone the wrist joint displaces, transferring the rotational energy into bat speed. Again, this was shown with great clarity in Nyman's 2-link robot example. No torque at the wrist joints or hands is required to make this work. It's just the dynamics of the swing.
>
> I think we're almost in agreement here. I just maintain, like Adair, that to turn this rotational energy into batspeed, you are actually applying linear forces to first order directed along the direction of the bat, and not torques at the bat handle.
>
> Finally, I guess I am missing your point on the lever arm. I believe you now agree that wrist joints aren't a major supplier of torque to the swing. If torque is being applied at the bat handle by differential forces in the hands, then that torque is given by
>
> Total torque about bottom wrist = Top hand force * lever arm from top hand to bottom wrist.
>
> To talk about torque without a lever arm doesn't make any sense from physics, since Torque = Force * lever arm. To increase any torque, you increase lever arm. Thus, again, if differential forces are important you would want to increase the lever arm between them to increase torque (leverage is not a physics term), i.e. split the grip.
>
> -JJA
>
> Hi JJA
>
> First, let me say that our disagreements have has led to interesting discussions of swing mechanics. I think it is now time that I "cut to the chase" and make an observation that should point out our remaining differences in what forces are at work in effecting the angular displacement rate of the bat.
>
> I contend that, depending on the actual displacement rate of the hand-path, "torque" is the major factor (70+ %) in generating bat speed with batters who extend their hands in a fairly straight path. I support this with the following:
>
> You stated, "I agree with your demonstration on the video. If you just thrust the knob of the bat at the ball, of course you don't get the whip effect. There is no disagreement with us there." -- In essence, we have agreed that for the bat to undergo angular displacement, the force (hand-path) must undergo angular displacement.
>
> Regardless of the batter's hip and shoulder rotation, there is no "whip effect" or "flailing action" of the bat occurring from a completely straight hand-path. Applying force at a second point in the hand-path creates a lever arm and makes torque the major factor in generating bat speed from a straight thrust of the hands.
>
> Your thoughts
>
> Jack Mankin
>
>
>
Jack,

Well, it does appear we're whittling down our differences. I agree that there is no whip of the bat due to a completely straight hand-path. I furthemore agree that the hand path must undergo angular displacement in order for the bat to undergo angular displacement.

Our last issue is simply what forces and torques are applied to the bat during this process.

I will further agree that if a batter wanted to, he could create a linear hand path to the ball while rotating and hit the ball with the knob of his bat, although this maneuver is very awkward to perform. Furthermore, if you do this while rotating hard, it is almost impossible to keep the barrel of the bat from rotating. Try it yourself. If I rotate hard, the bat barrel tries very hard to rotate. I myself can't do it without the bat barrel rotating a few degrees. My wrists aren't strong enough to keep the barrel from rotating. This is the whip effect, even though I am trying my hardest to make a linear hand path and restrain it.

It sounds like you view this as the swing process, and then modify it by torquing the bat to create bat rotation. I simply don't view it this way. I view the swing almost like you do, the lower body and torso rotating, the hands in a near circular arc. My point (and that of Adair) is that this can be done with no torque applied to the handle of the bat. This circular motion can be created entirely with a linear force directed out the knob of the bat. This force vector thus also has a near circular path during the swing. However, a force vector having a circular path is not the same as torque.

-JJA