The DeltaCELT https://www.physicsfunshop.com/search?keywords=deltacelt A new elegant rattleback design where the indentations create an asymmetry in the distribution of mass that leads to rotation reversals when spun: 1) If spun clockwise, after about two full rotations, a complicated combination of friction, precession, and instability induced vibrations transforms the rotational energy into into end-to-end rattling (energy of oscillations) and then into rotational energy in the opposite direct

Enantiomorphic Rattlebacks: due to mirror reflection construction, one prefers to spin counter clockwise the other prefers clockwise. This behavior is related to an asymmetry in weight along the left/right symmetry axis of these beautifully crafted objects- the dark wood is Apple which has twice the density of the light colored Basswood(Linden). This asymmetry in weight induces an instability, quite like the vibrations that arise from an unbalanced tire, that transfers the rotational energy to t