the forces between grains of sand

July 13, 2009

If I asked you what makes water form into droplets, you might say surface tension, perhaps (for the more sciency) intermolecular forces like dipoles and hydrogen bonding. Most of us are comfortable with these strange little forces acting on the tiny, molecular level, but then how can we explain these clips:

This above clip is a high-speed video of falling sand, where the camera is falling at the same speed of the sand and thus can capture the “drops” of sand that form from the thin stream. The below clip shows an iron ball falling into sand.

A recent study by the Jaeger group at U. Chicago in Nature investigates (that Mark Trodden of Cosmic Variance summarizes) the interactions of sand particles. Jaeger’s group demonstrated the existence of surface tension forces roughly 100,000 times less strong than those of normal liquids on the sand and nanoNewton forces between the particles.

Not only is this research just plain cool, but it also illustrates how we’re still learning about seemingly everyday things like sand. Most often people see current scientific developments as incredibly specialized and unapproachable. Research like this reminds us of the science that we interact with even when we’re not looking for it.

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