Weeble

Weebles is a trademark for several lines of children's roly-poly toys originating in Hasbro's Playskool division on July 23, 1971. Tipping an egg-shaped Weeble causes a weight located at the bottom-center to be lifted off the ground. Once released, gravitational force brings the Weeble back into an upright position. Weebles have been designed to have a variety of shapes, including some designed to look like people and animals, among others.

The popular catchphrase, "Weebles wobble, but they don't fall down", was used in advertising during their rise in popularity in the 1970s and during successive relaunches in the early 21st century.

The Weebles 1971-2011 Price Guide and Index Book lists and shows every Weeble model made over the past 40 years. There are 21 peelable / 83 regular / 12 tumbling = 116 Weebles in total including all egg shaped sizes and variations made during 1971-1983. In 2010 Hasbro started making a new line of larger egg-shaped Weebles and had produced 42 new Weebles as of July 2011.

A wide range of accessories were available for the Weebles including vehicles, buildings and furniture. Some sets had a theme to them, such as the Weebles circus set.

A Weeble is shaped like an egg—in order for the physics principles to work as intended, the shape must have a bottom which is a more or less smooth (unfaceted) (to allow the Weeble to roll) and from the central vertical axis the shape must be nearly cylindrically symmetrical (that is, any plane cut through the vertical axis line must produce close to the same profile). Next, the shape must be filled with two basic types of unmixed solids, and the volume of the lighter solid must be greater than that of the heavier solid. Next, the overall shape must have constant positive curvature. Next, the relationship between the heavy solid and the light solid must be such that any orientation of the object off of the vertical axis line must cause the object's centroid to raise and to become offset. Lastly, the object must have only one position in which it can achieve stable mechanical equilibrium.

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