Researchers at the University of Twente in the Netherlands have created an experiment that demonstrates how sand can exhibit liquid-like properties. They provide beautiful photos and a 1k-frame/sec movie of a marble-size steel ball dropping onto loose, fine sand. This may aid geophysicists in understanding what happens when an asteroid smashes into a planet.
This reminds me of attempts in the 1970's in graduate school and at my first job at a R&D organisation to use computers to model the flow of fluids. It was simple when we tried simple things--rivers and streams, waves in very deep water, hydraulic jumps, etc. Proved impossible for anything "complex". 99% of fluid flows are "complex". This movie helps me appreciate why.