Photo of stress in a two-dimensional granular material. Granular materials, such as sand, behave in a surprising way: they can flow like a liquid, yet carry weight like a solid.Images such as shown reveal the otherwise hidden and intricate force network between the particles, and continue to give surprising new insights in the interesting behavior of something as common as sand.
Source: Duke Graduate Student Photo selected “Picture of the Day” by NSF, Dept. of Physics at Duke University
