From Dynamics of Water Entry by Tadd T. Truscott, Jeffrey M. Aristoff, Alexandra H. Techet & John Bush, Massachusetts Institute of Technology.
The videos illustrate the hydrodynamics associated with water-entry of spheres, which can be highly variable with respect to their material and kinematic properties. The first video, contrasts the nature of impact between a hydrophilic and hydrophobic sphere and illustrates how surface coating can affect whether or not an air cavity is formed. The second one, illustrates how spin and surface treatments can alter the splash and cavity formation following water entry. The third one compares two millimetric nylon spheres impacting at slightly different impact speeds; the faster sphere fully penetrates the free surface, forming a cavity, whereas the slower sphere does not. The fourth series shows the instability of an elongated water-entry cavity formed by a millimetric steel sphere with a hydrophobic coating impacting at 600cm/s. Finally, a millimetric steel sphere with a hydrophobic coating breaks the free surface with an impact speed of 350cm/s.