Yeah, we need the high speed cameras... This is weird.. backspin behaves one way, topspin the opposite.

Iskandar

Conclusion
Changes between the trajectory of celluloid balls, which had been long used in table tennis, and newly introduced plastic balls were investigated in this study. Plastic balls demonstrated a higher coefficient of restitution than celluloid balls when the initial vertical velocities were higher. Moreover, the coefficient of friction was higher for plastic balls when the initial horizontal contact point velocities were lower. As a result, for slower balls with back-spin, as in the case of a service, plastic balls are expected to experience more deceleration upon collision with the table than celluloid balls. On the other hand, for faster balls with greater amounts of top-spin, plastic balls are expected to experience greater acceleration upon collision with the table than celluloid balls.

I am really confused now. I read that "poly" balls were polystyrene and that is how they got their name, even though I assumed "poly" was short for polymer. Now I read that Nittaku "poly" balls are ABS. So does poly mean polymer or polystyrene?