Astrojax

Astrojax is a skill toy consisting of three balls threaded on a length of string, with one ball fixed at each end and a third ball free to slide along the string between them. It was invented in 1986 by Larry Shaw, a physics graduate student at Cornell University, who developed the toy while experimenting with hex nuts and dental floss before refining it into its current form. Each ball is weighted internally with a metal insert that reduces its rotational inertia, letting the free center ball spin rapidly around the string without the string itself tangling as the player performs tricks. Play draws on techniques borrowed from juggling, yo-yo manipulation and lasso spinning, and basic maneuvers include vertical orbits, horizontal orbits and figure-eight or butterfly patterns traced by the moving balls. Beyond recreational play, Astrojax has also been used to illustrate physics concepts such as the conservation of angular momentum, since the changing radius and speed of the orbiting balls during a trick offer a hands-on demonstration of the underlying mechanics.