Water entry of spinning hydrophobic and hydrophilic spheres

An experimental investigation of the trajectories, forces and cavity formation behind spinning hydrophobic and hydrophilic spheres is presented. Several cases are also presented for non-spinning spheres which are half hydrophobic and half hydrophilic. Data from high speed imaging are processed using advanced data techniques to gain accurate position, velocity and acceleration trends for the spheres as they descend and curve along their trajectories. The data show that an increase in lateral (sideways) force corresponds with the asymmetric cavity formation around the spinning or half-and-half coated spheres. Despite the lack of cavity formation, the slower translating and rotating hydrophilic spheres still move along a curved trajectory, but with less lateral displacement, velocity and acceleration, thus indicating that spin induces less lateral force compared to asymmetrical cavity formation. © 2011 Elsevier Ltd.