Running up a sand dune

Running up a sand dune is a challenging task due to several factors. First, sand fluidizes when an external force exceeding the material yield stress is applied. Second, at the angle of repose, the sand pile is in a metastable state, such that small perturbations will cause fluidization. Ongoing studies show that sand specialist lizards exhibit lower performance decrements than desert generalist when running up inclined sand. Preliminary evidence suggests that these differences are largely correlated with different impact angles of the feet relative to the sand, indicating that differences in foot movement can have dramatic effects on running ability. In this study, we experimentally examine the vertical impact force of a flat plate (1 in x 1 in) against a glass beads with varying plate and substrate angles. The plate impacted the substrate at 0.6 m/s with a force sensor attachment. Here, we find that impact at higher angles reduces the peak force, with impacts at the angle of repose producing 55% less force compared to impacts on a flat bed. Greater substrate incline also increases the time to reach the peak force. This is largely due to earlier contact time which causes the sand to fluidize sooner. Results from impacts with different plate angles will also be discussed.