Ever wonder why sand can both run through an hourglass like a liquid and be solid enough to support buildings? It’s because granular materials – like sand or dirt – can change their behavior, or state. Researchers from North Carolina State University have found that the forces individual grains exert on one another are what most affect that transition.
Physicists have explored the changing behavior of granular materials by comparing it to what happens in thermodynamic systems. In a thermodynamic system, you can change the state of a material – like water – from a liquid to a gas by adding energy (heat) to the system. One of the most fundamental and important observations about temperature, however, is that it has the ability to equilibrate: a hot cup of tea eventually cools to match the temperature of the room. (more…)