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well if it's the same diameter and mass, but thinner, then it's gonna be more reluctant to spin, no?
Yes, undoubtedly. An analogy would be that a heavier object is more reluctant to movement. So if you convert the same energy to the rotation of those 2 TT balls (same shape and weight), so that now they have the exact same rotational energy, then the one with thinner shell will rotate slower. Which also means that if they rotate equally fast, then the one with thinner shell will have more rotational energy, and may appear to us as having a heavier spin.
But with the very same stroke you will not impart the very same energy to those 2 balls, imo. An analogy, if you take TT ball and golf ball and throw them with the exact same movement, say as fast as you can, the golf ball will have significantly more energy. They will have very very similar speeds though, at least initially. This analogy is a bit imprecise, because it is not really a collision between those balls and the hand, but I am using it because it is so easy to visualize. Similarly, with the very same stroke, the 2 TT balls will not receive the exact same rotational energy, because what happens between the ball and bat has elements of both a bounce and of a throw. After all, we tend to speak about the dwell time and the throw angle. So, imo, the 2 TT balls will have different rotational energy (the one with thinner shell will have more rotational energy), and similar spin (speed of rotation). Perhaps not as similar as the thrown balls (TT ball and golf ball), I can't quantify.
I thought that the ball with thicker shell will get a bit more (faster) spin initially. But I simply don't know. What Zwill said is very interesting. It may be, that due to, let's call it, details of how the imparting of spin actually exactly happens between the ball and bat, that the ball with thinner shell, may even get more spin (not only more rotational energy). I don't know. Hopefully Someone can explain eventually.
Anyways, Igor says the one with thinner shell rotates faster. We don't know how he measured. Maybe they rotate almost equally fast, but the one with thinner shell he perceived as a heavier spin, as I mentioned above...
I hope it's OK I replied to this question. It's possible the differences are negligible. It is absolutely clear it has not much practical TT meaning. But where do you draw the line? Finally, I will not reply to incoming accusations in this thread.