  In this paper we study the transient surface cavity which is created by the
controlled impact of a disk of radius h0 on a water surface at Froude numbers
below 200. The dynamics of the transient free surface is recorded by high speed
imaging and compared to boundary integral simulations. An excellent agreement
is found between both. The flow surrounding the cavity is measured with high
speed particle image velocimetry and is found to also agree perfectly with the
flow field obtained from the simulations. We present a simple model for the
radial dynamics of the cavity based on the collapse of an infinite cylinder.
This model accounts for the observed asymmetry of the radial dynamics between
the expansion and contraction phase of the cavity. It reproduces the scaling of
the closure depth and total depth of the cavity which are both found to scale
roughly proportional to Fr^{1/2} with a weakly Froude number dependent
prefactor. In addition, the model accurately captures the dynamics of the
minimal radius of the cavity, the scaling of the volume Vbubble of air
entrained by the process, namely Vbubble/h0^3 proportional (1 +
0.26Fr^{1/2})Fr^{1/2}, and gives insight into the axial asymmetry of the
pinch-off process.
