Physics of the PhiTOP

The PhiTOP® (or ΦTOP®) is a physics toy designed not only to act as a spinning top but also to appeal to the eye and to the scientifically curious mind. It is currently made in two versions, one from solid aluminum and the other solid brass. Each top is highly polished, and is elliptical in one cross section and circular in another. It is therefore a prolate ellipsoid or a spheroid, as indicated in Fig. 1. Its name derives from the ratio of the lengths of the major to minor axes, which is equal to the golden mean Φ = (1+ √5)/2∼1.618. It functions in the same way as a spinning egg or a spinning football in that it rises on one end if it is initially set spinning at sufficient speed with its long axis horizontal. The center of mass rises in an unexpected and somewhat mysterious manner, an effect that it also shares with a tippe top.