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Re: Re: Question for the Scientists

Posted by: Jack Mankin (mrbatspeed@aol.com) on Wed May 12 19:58:28 2004

Hi All

This is a very important topic. I will address each of JJA’s statements separately.

JJA >>>This is a very difficult question to answer in a thread. I refer you to Dr. Adair's full chapter on this, including many informative graphs including his modeled swing path, which by the way, is not that far from a circular path. I'll give you a couple of ideas to think about.

Dr. Adair's model is that there is little torque applied to the bat, but instead a linear force is applied in the direction of the bat handle. Think of an arrow sticking out the bottom of the bat. That represents the direction of the force applied by the hands on the bat, in his model. Swing a bat and feel the pressure on the bottom of the lead hand near the knob. This is the force that Dr. Adair is describing that is being applied to the bat. As an aside, this is why one can swing a bat with the lead arm only with significant bat speed. It does not require differential forces (i.e., torque) of the hands to generate bat speed. <<<

My Reply: You stated, “Think of an arrow sticking out the bottom of the bat. That represents the direction of the force applied by the hands on the bat” -- I seriously do not understand how you could study this clip and say that the hands are directing their force down the length of the bat (the way the arrow points). The rotation of the lead-shoulder is clearly pulling the lead-hand across (about 90 degrees) the bat’s length. The lowering of the back-elbow causes the top-hand to pull in the opposite direction (torque – hands applying force from opposing directions).

NOTE: A batter with linear mechanics does accelerate the hands (and knob) as JJA described (with the arrow). However, this is a clip of a batter exhibiting rotational transfer mechanics. His hands stay back (applying torque) and allow shoulder rotation to accelerate the hand-path. That is how he generates a CHP.

Adair and I have always agreed that bat speed is generated from the angular displacement of the hand-path. However, Adair states in his book (and my discussions with him), that the arc in the hand-path only occurs early in the swing. The hand then straightens out and extends forward. I maintain that the hands remain in a circular path to generate bat speed all the way to contact.

My tests reflect, that given time and a long enough hand-path, bat speeds exceeding 70 mph can be attained with just one hand (note: torque was being applied by the wrist – no steering-wheel knob). However, during a “real swing,” the hand-path is only 22 to 26 inches to contact with rotational mechanics. This length of hand-path (minus torque) generates speeds in the 50 mph category.

Adair and I agree that the hand-path generates a good portion of the bat speed. The question then becomes - what force applied to the bat accounts for the balance of the bat speed developed. Adair claims it is from the transfer of kinetic energy (developed from the body moving forward about 18 inches at 7 to 8 mph DURING the swing) to the bat as the hands slow to a stop (the ”Whip Effect”). --- With the rotational model I defined, the body rotates around a stationary axis DURING the swing and the continuous application of torque throughout the swing account for the balance.

JJA >>> What I believe the root conceptual difficulty here is that this force is applied in a direction that is continually changing. Indeed, as Jack correctly pointed out - and I give him full credit for being the first to make this observation - the hands have a (nearly) circular trajectory. Strange, isn't it. A force that is being applied in a circular direction. Isn't that identical to a torque being applied to the bat? From a purely physics viewpoint, no. The video of Sosa is entirely consistent with force being applied primarily in the direction of the bat. <<<

My reply: No JJA, a force that is being applied in a circular direction IS NOT identical to torque being applied to the bat. The direction of force from the CHP is directed down the length of the bat – like swinging a bat on the end of a rope. To apply torque to a bat requires that the hands apply force from opposing directions. Although both are present in a good swing, these are two completely different principles. Torque can be applied while the hands are moving straight (no CHP).

JJA, by applying torque to the bat, I can accelerate the hand-path in a straight line and generate significant bat speed long before the goat hits the end of the rope. Excuse me, -- where the supposed whip-effect is to take place.

JJA >>> Why this question is so difficult to answer is that, despite attempts to ridicule this line of reasoning, it involves biomechanics of which I do not purport to be an expert. Between frames 1 and 10, his shoulders have rotated significantly. (Difficult to tell, but it looks in excess 40 degrees.) This rotational energy in the upper torso obviously gets transformed into the arms which then transform energy into the bat but the details of how this is precisely done is beyond my knowledge. <<<

My reply: You stated, “This rotational energy in the upper torso obviously gets transformed into the arms which then transform energy into the bat but the details of how this is precisely done is beyond my knowledge.” JJA, understanding precisely how the body’s rotational energy is transferred into bat-head acceleration is why I spent hundreds of hours testing in physics labs. As I have stated before, the chair of three different Physic’s Departments helped me define the forces doing work on the bat that could cause the angular displacement we see in this clip. --- Torque was their term. I defined it as “Top-Hand-Torque” because it appeared to be the most active hand during that part of the swing.

JJA >>> I actually think of this problem as a two link robot, which Nyman displayed so superbly in a recent post. That example shows how rotational energy of the first link (body) can generate significant linear velocity on the second link (read bat speed) when no torques are applied to the second link (bat via wrists). Although it is certainly a gross approximation, I think it is a very useful one and probably the best example of describing Dr. Adair's model that I can think of without getting too mathematical.<<<

I have no comment since I have not had the opportunity to study his robot.

Jack Mankin


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