Sorting sand from sugar is a classic chemistry challenge — dissolve the mixture in water, filter out the sand, and evaporate the water to recrystallize the sugar. But spontaneous stratification offers a different, mesmerizing approach.
The experiment is simple: sift some fine sand, hopelessly mix it with coarse sugar (colourfully dyed for maximum visual impact), then pour the mix out. The different sized grains have different angles of repose, which is the steepness a pile of material will naturally set before spilling in an avalanche. While slight, the difference is enough to create layering, or stratification, between the two materials.
By looking at a mathematical model of the scenario, the finer grains infill between the layers of courser grains, building up stratified layers. The Simons Foundation has produced a full video on the process, including instructions on how to run the experiment at home with basic materials.
Tip via Scientific American. Read more about it here. Images extracted from the Simons Foundation video. Looking for more kid-friendly home experiments in material science? Try mixing up a batch of sticky, silky "moon dust."