Fig. 8. Sketch illustrating the definitions of (a) the cavity velocity U_c and (b) the velocity of the retracting cavity U_cr. (c) Ratio of the cavity velocity U_c and the impact velocity U_jet, compared to the expected value of 0.5. (d) U_cr divided by the capillary velocity scale ; average values for each liquid are statistically similar, indicating that the retraction of the cavity is governed by capillary forces. For each liquid, bold coloured symbols represent average values of light symbols.