1. Introduction
In this paper the two-dimensional dynamic behaviour of a loaded hoop is investigated, by which is meant a heavy rigid hoop to which a heavy particle is fixed on the rim.
The hypothetical problem of a loaded massless hoop rolling without slipping on a horizontal surface has been used for very many years as an interesting class-room problem for planar motion of rigid bodies, and was first published by J.E. Littlewood [1] in 1953 in “A Mathematician’s Miscellany”.
The same problem is considered by Tokieda [2], whose analysis is based on the geometric aspects of the motion. Both Littlewood and Tokieda conclude that the hoop will hop after rolling through 90∘ after starting from rest with the particle at the highest point of its cycloidal path.
Subsequent papers by Butler [3] and Theron & du Plessis [4] considered the question of whether the massless hoop could hop or not. The motion of real hoops, with mass and assumed to be rigid, were published by Pritchett [5], Theron [6] and Liu [7], also with some emphasis on the question of hopping.
Tokieda [2] reports having witnessed an experiment by Fred Almgren [8] in which a hula-hoop was loaded with a battery and hopped as predicted by Littlewood, namely that the hoop leaves the ground when the radius to the particle is approximately horizontal and the particle is moving downwards. Pritchett [5] also shows a stroboscopic photograph of the same phenomenon, in which a plastic hula-hoop is loaded with brass rods. Theron’s article [9] on elastic hoops is the first to develop a model which gives a reasonable explanation of the abovementioned phenomenon, by taking the elasticity of the hoop into account.