This is in the lab for a reason. If you find it "harder to read than TGM", don't read it.
For anyone that still doesn't see the center of mass or "center of gravity" of an object (Cg(m)), here's an example:
Imagine a baseball bat being carved on a lathe. The finished bat is symmetrical in cross section. It would be very easy to cut the bat in half at any circumference and find the longitudinal centerline of the bat or the center for that circle. When a bat is finished, you could crank the lathe up to 1000 mph, and the bat would not waiver. But, since the bat is heavier on one end, you could balance it on a balance beam to help find the bat's Cg(m). One laser fires longitudinally through the center line of the bat and one fires through the balance point established by the balance beam. The intersection of those beams would be the Cg(m).
A golf club on the other hand is asymmetrical in cross section in addition to being heavier on one end. The longitudinal centerline for the bat is the same as this example in a golf club: "The spot on the Clubface through which a plumb-bob line would pass if suspended from the Grip area." As a result, the Cg(m) doesn't reside in the mass of the club. If this invisible, longitudinal centerline of the golf club was arranged on the lathe as was the center of the bat, you could crank up the speed of the lathe again. But, if the longitudinal centerline was the shaft, I'd suggest you go in another room when the lathe gets cranked up. Something's going to break loose, because the clubhead will wobble.
Additionally, the Cg(m) being mid body for a human has nothing to do with a pivot center. It's just a regurgitation of an intelligent sounding phrase: "center of gravity". Once the concept of Cg(m) is understood, its application to moment of inertia is important. Moment of inertia should always be discussed relative to an axis of rotation. This axis might run through the Cg(m) or it might not. The pivot axis does not go through the human Cg(m), making MOI and axis important in this case as well. In the golf club case, the MOI is usually discussed about the club shaft axis, since we have our hands attached to it. The clubshaft MUST leave the plane.
Yoda likes to use the analogy of someone throwing a hatchet at a wall. It's another example of something that doesn't rotate around it's shaft.
If you don't see the analogies above, shank you anyway for your time,
Ted Fort
P.S. Thank you, Thinkingplus, for the validation and suggestions. For anyone that doesn't know, she's the queen of physics.
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