When an intruder strikes a granular material from above, the grains exert a stopping force
which decelerates and stops the intruder. Many previous studies have used a macroscopic
force law, including a drag force which is quadratic in velocity, to characterize the
decelerating force on the intruder. However, the microscopic origins of the force-law terms
are still a subject of debate. Here, drawing from previous experiments with photoelastic
particles, we present a model which describes the velocity-squared force in terms of …

When an intruder collides with a granular material, the grains exert a stopping force which
decelerates the intruder. A macroscopic force law, dominated by av 2 drag term, is often
used to characterize this decelerating force. However, a description which connects this
drag force to grain-scale dynamics is still lacking, due in part to difficulty in obtaining
sufficiently fast data at the grain scale. We present experiments using photoelastic particles
and a high-speed camera, which capture the intruder dynamics and local granular force …