  In this study, we experimentally examine the behavior of a free falling rigid
sphere impacting normally onto, and penetrating into a quiescent liquid pool.
Parameters, which are varied include the impact velocity, the density, and the
diameter of the sphere. Observations of the sphere trajectory in time are made
using two orthogonally placed high-speed cameras, yielding the velocity and
acceleration vector through repeated differentiation of the time resolved
trajectories.
  Upon penetration, the sphere goes through three very distinct phases of
penetration, denoted as the submersion, deceleration and settling phase, each
clearly identifiable through either features seen in trajectory direction or in
changes of velocity. These phases exist for all impact Reynolds numbers and
density ratios investigated, and their respective duration remain astoundingly
constant in terms of dimensionless time. The motion of the sphere is analysed
using a scalar force balance for each of instantaneous drag and lift, yielding
quantitative estimates of the drag and lift coefficients throughout the
trajectory. The variation of these forces can be phenomenologically explained
by unsteady wake behavior arising from strong deceleration and through
transient asymmetry, leading to variations in trajectory curvature. Despite the
large trajectory randomness observed in repetitive experiments, there exist
strong commonalities in motion behavior.
