Abstract: A multi-function yo-yo switchable between operation as a fixed-axle yo-yo, a free-axle yo-yo, and a centrifugal-clutch yo-yo (i.e., a yo-yo which operates as a free-axle yo-yo when it spins sufficiently rapidly, and as a fixed-axle yo-yo when it spins sufficiently slowly). Within one or both of the fly disks is one or more rotational-speed governors, and about the axle is a cylindrical axle sleeve which is rotatable about the axle. Each governor is spring-biased to an inwards position where a contact pad on the governor contacts the axle sleeve, forcing the axle sleeve to rotate with the fly disks and axle. However, when the yo-yo spins sufficiently rapidly, the governors are thrown by centrifugal force to a radially-outwards position where the contact pads are not in contact with the axle sleeve so that the axle sleeve may rotate independently of the fly disks. A function control switch on the exterior of the yo-yo is easily accessible and allows rapid switching between yo-yo functions.

Abstract: A play object consisting of a larger ball with an open, substantially spherical-section cavity into which a smaller ball fits snuggly, yet is easily removable and re-insertable due to the diameter of the rim of the cavity being slightly smaller than the diameter of the smaller ball. The rim of the cavity is rounded. When the smaller ball is positioned in the cavity, it protrudes to roughly the spherical boundary defined by the larger ball to allow the combination to roll. When the smaller ball is removed from the cavity, the smaller ball is rollable, and the larger ball is relatively stable when placed on a flat surface with the cavity side down. Furthermore, multiple larger balls oriented with the cavity side downwards may be stacked. The balls are preferably soft, and their surfaces can be smooth, ribbed or furry. Ribbed larger balls provide the advantages of facilitating stacking, and obscuring deviations in the trueness of rolling produced by the lip of the cavity.