  The presence of ambient air in liquid-slamming events plays a crucial role in
influencing the shape of the liquid surface prior to the impact, and the
distribution of loads created upon impact. We study the effect of trapped air
on impact loads in a simplified geometry, by slamming a horizontal flat disc
onto a stationary water bath at a well-controlled velocity. We show how air
trapping influences pressure peaks at different radial locations on the disc,
how the pressure impulses are affected, and how local pressure impulses differ
from those obtained from area-integrated (force) impulses at impact. More
specifically, we find that the air layer causes a gradual buildup of the load
before the peak value is reached, and show that this buildup follows inertial
scaling. Further, the same localised pressure impulse at the disc centre are
found to be lower than the corresponding (area-integrated) force impulse on the
entire disc. While the (area-integrated) force impulses are close to the
classical result of Batchelor (1967, section 6.10) and Glasheen & McMahon
(1996), the localised pressure impulses at disc center, where the trapped air
layer is at its thickest, are found to lie closer to the theoretical estimation
by Peters et al. (2013) for an air-cushioned impact.
