>>> Hi Jack
I have a hitting video were the instructor uses a short bunji cord. he spreads his hands about 6 inches apart holding each end of the cord .He pulls the cord taut then demonstrated a swing and stopped at contact. He never allowed any slack in the cord thru out the swing .my question is do you think this is a good way to teach the correct forces on the bat handle? If rearward bathead acceleration and a circular hand path were kept in mind <<<
I would say that spacing the hands 6 inches apart might be effective as a teaching aid. It should help the student understand how torque applied at the handle can induce the bat-head to rotate about a point between the hands. However, I would not recommend this spacing be used for teaching the actual swing.
We must keep in mind that there are two physic principles that governs the bat's angular acceleration. One is the handle torque we are discussing. The second principle that induces bat speed is the swinging of the bat-head that occurs from the angular displacement rate of the hand-path (The "Pendulum Effect" of a CHP). Spacing the hands wider apart may increase the torque factor but would greatly restrict the pendulum effect.
The maximum pendulum effect occurs when force of the CHP is applied at a single point, as when the bat is swung with one hand. With two hands on bat, forces are applied at two separate points, which provides torque while restricting the bat from freely rotating about a single point. This restriction is amplified when the batter's arms and wrist are tense and ridged during the swing.
I stress to my students that to attain maximum results from both torque and the pendulum effect - their arms, wrist and hands must remain as loose and fluid as possible. Much of the tenseness in the arms can be eliminated by allowing the rotation of the shoulders to 'swing' the hands to contact rather than getting the arm muscles involved. Obviously, the muscles of the arms (mainly the back-arm) are used to apply torque, especially during the initiation phase. However, most of the push/pull of the forearms should also come from shoulder rotation.
Below is a link to a "Sports-Science" article on this topic. It reads very similar to the conclusion of my report I sent to Professor Adair in the early 1990s regarding my rotational swing model.
Bat Speed and Hitting