A roly-poly toy, roly-poly doll, round-bottomed doll, tilting doll, tumbler, wobbly man, wobble doll, or kelly is a round-bottomed toy, usually egg-shaped, that tends to right itself when pushed at an angle, and does this in seeming contradiction to how it should fall.
Different toy manufacturers and different cultures have produced different-looking roly-poly toys: the okiagari-koboshi (èµ·ãÂÂä¸ÂãÂÂãÂÂå°Âæ³Â師, "take a spill, get up, and arise"), Kokeshi doll and some types of Daruma doll of Japan, the nevðlyashka (ýõòðûÃÂÃÂúð, "untopply") or van'ka-vstan'ka (òðýÃÂúð-òÃÂÃÂðýÃÂúð, "Ivan-get-up") of Russia, and Playskool's Weebles. Such toys' self-righting characteristics have come to symbolize the ability to have success, overcome adversity, and recover from misfortune.
Traditional Chinese examples (called ä¸ÂÃ¥ÂÂç¿Â, bù dÃÂo wÃÂng) are hollow clay figures of plump children, but "many Chinese folk artists shape their tumblers in the image of clownish mandarins as they appear on stage; in this way, they mock the inefficiency and ineptitude of the bureaucrats".
Fisher-Price, a well-known toy manufacturer, recommends roly-poly toys for small children just developing motor skills; a child can bat at it without its rolling away.
The toy is typically hollow with a weight inside the bottom hemisphere. The placement of this weight is such that the toy has a center of mass below the center of the hemisphere, so that any tilting raises the center of mass. When such a toy is pushed over, it wobbles for a few moments while it seeks the upright orientation, which has an equilibrium at the minimum gravitational potential energy.