Posted by: Jack Mankin (MrBatspeed@aol.com) on Thu Mar 9 16:35:40 2006

>>> Jack,

Why do you believe that a weight shift isn't a power source to the swing? Not to agrue the linear vs rotational, but to better understand how you came to this conclusion.

I've been studying the weight shift of hitters. As you know this is usually a shift of the hips prior to going into rotation. You believe that all linear movement stops prior to rotation, but video shows it's a smooth transition between the two.

So far the study has been inclusive. While some have a more pronounced weight shift, other have a weight shift to a lesser degree. I'm starting to wonder how much weight actually plays during the swing. I swing best with a no stride, I have a slight shift. But, compared to some hitters with a longer stride this shift is rather small, although I still hit the ball hard. <<<

Hi Shawn

You state, "I've been studying the weight shift of hitters. As you know this is usually a shift of the hips prior to going into rotation. You believe that all linear movement stops prior to rotation, but video shows it's a smooth transition between the two." The hips may start to rotate as weight shift ceases, but that rotation comes from muscle contractions in the pelvis region rather than from momentum transfer.

From my own experiments and discussions on the Conservation of Momentum with Physics Departments, I found that any gain in hip rotation attained from a linear weight shift to be negligible. Most of the proponents of the weight shift theory use a form of the following example to support their position. However, a close examination of the example as applied to the baseball swing shows their conclusions are flawed.

"Conservation of Momentum Example:

In a defined system all momentum is conserved. Let's define our system as a cue-ball and 8-ball. Imagine that the cue-ball is already rolling on a nearly frictionless surface and the 8-ball is stationary. This is our system-two billiard balls. As the cue-ball strikes the 8-ball, the 8-ball receives its momentum and now the cue ball is motionless. Momentum is transferred and conserved. The 8-ball moves along and strikes a wooden block that moves forward. In this new two-object system the block has moved forward taking momentum from the 8-ball that is now motionless because it has transferred all of its momentum. The block then moves forward and clips the blade of a fan, which begins to rotate, accepting the momentum from the block, which slows down considerably as a result of the transfer of momentum."

I fully agree with this statement in the example: "As the cue-ball strikes the 8-ball, the 8-ball receives its momentum and now the cue ball is motionless. Momentum is transferred and conserved." But now let us apply this principle to the baseball swing. Let the cue-ball represent the velocity of the hips and the 8-ball represent the blocking action of the lead-leg.

When the lead-leg stops the hips, "the 8-ball (lead-leg) receives its momentum and now the cue ball (hips) is motionless. The lead-leg (and ground) absorb the hips momentum and ?Momentum is transferred and conserved." The hips have just started to cock open (from the pelvic muscles) and the motionless hips (zero linear velocity) have no linear momentum left to contribute to further hip rotation if that were even possible.

You state, "So far the study has been inclusive. While some have a more pronounced weight shift, other have a weight shift to a lesser degree. I'm starting to wonder how much weight actually plays during the swing. I swing best with a no stride, I have a slight shift. But, compared to some hitters with a longer stride this shift is rather small, although I still hit the ball hard." Shawn, if linear momentum contributed significantly to a more powerful rotation, would we not see all the top power hitters taking longer and more aggressive strides But we don't. Their strides are getting shorter, softer and shifting less weight forward. What does our commonsense tell us?

Jack Mankin