Angle of Repose is a beautiful exhibit fashioned from a large circular piece of diamond-plate metal, several handfuls of fine sand, and a large circular plexiglass plate. The plates are fixed to each other, and the visitor is invited to rotate the plates around a central fixed point.
As the plates turn, sand which has fallen to the bottom is lifted to the top where it then trickles down through the grooves in the diamond-plate surface.
The sand pours over the grooves like waves, rippling as it follows the angle of repose to the bottom of the plate.
(c) The Exploratorium, 1996