Flip over a soda can, and spin the printed top. The top can spin for over three minutes with a good start. The concave shape of the bottom of a soda can provides an excellent base for a top. As long as the center of gravity of the top is below the tip on which the top spins, the top can spin for a very long time. My initial design of a top for an inverted soda can had the center of gravity above the top tip, and that top-heavy top could only spin for about 30 seconds with a good start.