The mean velocity of nylon spheres transported in a horizontal water pipe

Large numbers of nylon spheres of different sizes, but all of relative density 1·20, were inserted in turn into a Perspex water pipe and their passage timed. Their mean velocity was less than that of wax spheres of neutral buoyancy examined in earlier work. Nylon spheres of diameter one-third of the pipe diameter travelled with the same mean velocity as the water; when this ratio was reduced to one-tenth, the mean velocity of the spheres was a minimum. The dispersion in the mean velocities of the nylon and the wax spheres was almost the same. The nylon spheres travelled more slowly than loaded polythene spheres of the same size and density.