  In the corresponding fluid dynamics video, created for the APS DFD 2012
Gallery of Fluid Motion, we show high-speed videos of 2D granular impact
experiments, where an intruder strikes a collection of bidisperse photoelastic
disks from above. We discuss the force beneath the intruder, which is strongly
fluctuating in space and time. These fluctuations correspond to acoustic pulses
which propagate into the medium. Analysis shows that this process, in our
experiments, is dominated by collisions with grain clusters. The energy from
these collisions is carried into the granular medium along networks of grains,
where is it dissipated.
