Posted by: () on Sat May 8 23:17:20 2004

> >>> Thank you again. I do believe I now understand exactly where you're coming from. From your two examples, torque is applied to the bat by differential forces in the hands. In the one example, the top hand was essentially pushing the bat creating torque, while in the second example, the bottom hand was essentially pulling the bat, also creating torque and thus bat speed. Combining a push-pull action with the hands unquestionably applies torque to the bat.
>
> One important question remains. From your two examples, it appears that when torque is applied to the bat handle by the two differential forces, the wrists elongate. I cannot envision how one this can be avoided. It seems this is an inevitable consequence of applying differential forces to the bat by the hands.
>
> From my observations, the wrist position on most swings seems relatively fixed until just before contact when the wrists do elongate. If significant torque is being applied to the bat during the swing, then based on your examples the wrists should elongate or possibly contract during the swing. Since at cursory level they do not seem to do this, this appears to be a contradiction.
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> Can you please explain this apparent discrepancy? <<<
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> Hi JJA
>
> The fact that you observed “the wrist position on most swings seems relatively fixed until just before contact when the wrists do elongate” tells me you have studied clips frame-by-frame and have a keen eye. I would only add that the wrists remain relativity fixed in a “good” swing.
>
> While doing video analysis of hundreds of young player’s swings, I have found that the batters whose mechanics accelerate the bat linearly (knob first) exhibit considerably more flexing and then un-flexing of their wrists during the swing than good rotational hitters. The reason you noted the wrist of those good hitters remaining relativity fixed is because the angular displacement rate of their bat stayed more in sync with the angular rate of their hand-path. This is why using torque during initiation to accelerate the bat-head back toward the catcher before directing energy toward the ball is so important.
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> JJA, you ask intelligent and informed questions.
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> Jack Mankin
>
> Jack,

Thank you for the kind words, but unfortunately I don’t think you’re going to like the conclusions I’ve reached. I think by our recent discourse, we’ve agreed on the following:

1. Early on, you hypothesized that torque applied to the bat was a significant generator of bat speed.

2. You then performed the experiments described earlier in this thread that demonstrated that significant bat speed could be generated by applying torque to the bat handle via differential forces of the hands, either top hand or bottom hand.

3. By these experiments, you thus proved your hypothesis that a primary contributor to bat speed was torque applied to the handle via differential forces in the hands.

I believe and hope that I have provided a fair description of precisely what you did. If I haven’t, please correct me where I have gone astray.

If this chain of reasoning is a fair representation of your position, I unfortunately conclude that point 3 does not necessarily follow from points 1 and 2. Although your experiments did prove that torque applied to the bat can provide significant bat speed, it does not follow that torque applied to the bat is actually present in a real, non-experimental swing.

You hypothesized earlier in this thread that torque is applied to the bat evenly throughout the swing. Unfortunately, your experiments showed (proved?) that whenever torque is applied to the bat, the wrists were elongating or possibly contracting. Since we have agreed that in good swings the wrists do not elongate or contract except just before contact, it follows that we reach the opposite conclusion, that little torque is applied to the bat by the hands throughout the swing.

There is no question torque is a major contributor to good swing mechanics. The rotation of the body is achieved by strong torque generated by the torso that is ultimately transmitted to the ground via the feet (which is why the front foot sometimes rolls over in the swings of power hitters.) The issue here is whether torque is applied to the bat via differential forces in the hands. I believe your experimental data is insufficient to prove this point, and in fact points to the opposite conclusion that little torque is applied to the bat via the hands in the swing of good players. Your experiments have helped validate – rather than repudiate – Dr. Adair’s swing model.

-JJA
Ph. D. Electrical Engineering, University of California, Berkeley
Senior Engineering Fellow, major aerospace firm
Several patents and papers in the area of dynamics and controls