  When a rigid body collides with a liquid surface with sufficient velocity, it
creates a splash curtain above the surface and entrains air behind the sphere,
creating a cavity below the surface. While cavity dynamics have been studied
for over a century, this work focuses on the water entry characteristics of
deformable elastomeric spheres, which has not been studied. Upon free surface
impact, elastomeric sphere deform significantly, resulting in large-scale
material oscillations within the sphere, resulting in unique nested cavities.
We study these phenomena experimentally with high speed imaging and image
processing techniques. The water entry behavior of deformable spheres differs
from rigid spheres because of the pronounced deformation caused at impact as
well as the subsequent material vibration. Our results show that this
deformation and vibration can be predicted from material properties and impact
conditions. Additionally, by accounting for the sphere deformation in an
effective diameter term, we recover previously reported characteristics for
time to cavity pinch-off and hydrodynamic force coefficients for rigid spheres.
Our results also show that velocity change over the first oscillation period
scales with a dimensionless ratio of material shear modulus to impact
hydrodynamic pressure. Therefore we are able to describe the water entry
characteristics of deformable spheres in terms of material properties and
impact conditions.
