Extravagant viscoelastic effects in the Worthington jet experiment

A sphere is located several centimetres above the free surface of a liquid contained in a cylindrical vessel. It is released under gravity and the resulting deformation of the free surface of the liquid is recorded. In the present work, particular attention is paid to the case when, for a mobile Newtonian liquid, a vertical jet of extravagant length is created, following the formation of an initial crater. The effect of the container dimensions on the length of this jet is analysed and the conditions under which the jet length is unaffected by the depth of the liquid and the radius of the cylindrical vessel are noted. In the present experiments, the length of the vertical jet can be as high as 300 cm for a Newtonian liquid. When the test fluids are made slightly viscoelastic by adding very small concentrations of a high molecular weight polyacrylamide, it is found that the jet length can be reduced by an order of magnitude. We assign this extravagant reduction in height to the extensional viscosity characteristics of the polymer solution and the simple falling-sphere technique under discussion is proposed as a convenient cleans of estimating ''resistance to extensional deformation'' in the case of very mobile elastic liquids.