A roly-poly toy, tilting doll, tumbler, or wobbly man, is hollow inside with a weight placed at the bottom. The toy's center of mass is below the geometrical center of the bottom sphere. Thus the toy has a minimum potential energy and is at stable equilibrium when it is in the upright position. Many cultures and countries have their own version of a roly-poly toy. Shown here is a traditional Russian Nevalyashka (Nevaliashka) toy. 1 of 3.