Relaxation processes in hourglasses
The flow of sand through an hourglass, or a capillary, shows an interresting behaviour.
Here is a film sequence of the flow of 5 different types of sand.
100 microns glass
180 microns glass
220 microns glass
400 microns rough glass
Booming dune sand
Below is a photo of the experiment where we studied the flow of sand.
C. T. Veje and P. Dimon,
Power spectra of flow in an hourglass,
Phys. Rev. E, 56 4376 (1997)
[gzipped ps (300 k)]