Originally Posted by AtomicDumpling
I just saw this comment and boy are you ever wrong about that.
From the linked page: "When you hold a bat with your hands at the bottom of the handle (a normal grip), the COP is located about six to eight inches from the fat end of the bat. If you choke up on the bat, the COP moves closer to the fat end. That's because the location of your top hand is the place you want the bat to pivot. Changing your hand's position on the bat changes where that pivot point is, which therefore changes the position of the COP to one that corresponds to the new pivot point."
Did you read your own references AD? Here'es a quote from http://www.acs.psu.edu/drussell/bats/cop.html Emphasis
added by me.
COP and the Sweet Spot - what location "feels" best?
So, there is pretty overwhelming evidence that the COP has nothing whatsoever to do with the measured performance of a baseball or softball bat.
However, from its definition as being the impact location that results in zero net force at the pivot point, the COP is still often referred to as being the "sweet spot" at least in terms of feel. Hitting the ball at the center-of-percussion on the bat should minimize the sting felt in the hands. Early research by Brody and Noble suggests that the best place for the ball to impact the bat with minimal force exerted in the hands is between COP relative to the 6-inch point on the handle and the node of the first bending mode of vibration. Robert Adair has long argued that its only the location of the node of the first bending vibration of the bat which influences feel. Rod Cross conducted numerous experiments on bats and tennis racquets and concluded that the most comfortable location is somewhere between the nodes of the first two bending modes, with the location of the node of the second bending mode being more important. The issue is somewhat controversial and has raised some interesting banter back and forth between holders of the various viewpoints.
It is true that the COP is the location where no net force is exerted at the pivot point. However, the recently discovered fact that the actual pivot point at the instant of collision is not on the hands under the handle, but about 2.5 inches completely beyond the end of the handle, renders the COP relative to the 6-inch point on the handle irrelevant. If the defacto pivot point during the collision is not on the handle, then there is no point on the handle where the net force is exactly zero and the COP is meaningless as a definition of the sweet spot.
Recent experimental evidence for hand-held tennis racquets[18-19] agrees with the results for baseball and softball bats. The location of the pivot point is not under the hands. Thus, the center-of-percussion relative to a pivot point on the handle is not representative of the actual playing conditions and cannot be the "sweet spot" location that feels best.