Rattleback

thingiverse

This antique novelty spins with ease in one direction, but refuses to turn the opposite way. Watch as it rattles before spinning in the opposite direction! Prior to discovering that a light sanding was essential for this design to function properly, I spent a week creating my own version. Despite this, I thought I'd share my experience. To use, place on a smooth surface with the curved side down and flick one end to set it spinning. Observe its movement when flicked in both directions and analyze its shape for reasons behind this behavior.