* Astronomy

Penn Physicists Develop Force Law for Granular Impacts: Sand, Other Granular Matter's Behaviour Is Better Defined
Sand.  A single grain is tiny, but solid, and shares the physical properties of other solid matter.  But pack or transport millions of grains together - as modern society does with coffee grounds, flour and industrial chemicals - and granular materials act differently, baffling engineers.  They take the shape of their containers and flow freely, like liquids.  In certain circumstances, they exert pressure like a gas.  The basic lack of behavioural knowledge contributes to wasted resources and energy, as well as erosion and other natural phenomena.
Now, researchers at the University of Pennsylvania have devised, for the first time, a mathematical formula to measure the impact force of objects dropped into granular matter, clarifying its physical behaviour not as solid-, liquid- or gas-like but with its own distinct and verifiable physical properties.

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