Change of a Viscoelastic Sphere to a Torus by Random Impacts

When a small (< 2.5 g) ball of silicone putty was put into a vibrating cylinder, it first bounced around like a rubber ball. After some time the motion produced by the random impacts caused the sphere to change to a torus, and ultimately it broke up into smaller “dog bone” shaped pieces. If the size of the initial sphere was increased to 4–5 g or more, the spherical shape remained stable for many hours. When the initial shape was changed from a sphere to a cube to a prism, the minimum critical size that would form a stable sphere increased from about 3 to 6 to 20 g, respectively. The formation of the torus is due to the combined effect of the spectrum of relaxation times of the material, the short time of impacts with the wall, and the tendency of a body in free flight to rotate around the axis having the highest moment of inertia.