Hard granular materials — sand, gravel, glass beads, and so on — can flow, but, in narrow regions or under large forces, they can also jam up, essentially turning into a solid. Soft particles can also flow and jam, but do so under different conditions than hard particles. One group of researchers used a custom-built rheometer to measure jamming in soft particles like the hydrogel beads pictured here. They found that they could extend existing models for jamming in hard particles, but they had to rescale the mathematics to account for the way soft particles change their shape under pressure. (Image credit: Girl with red hat; research credit: F. Tapia et al.; via APS Physics)
Jamming Soft Grains
