Science Sidebar: Kinetic Sieving or Spontaneous Stratification

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This week we are going to be separating mixtures using laboratory techniques. It turns out that there are geological processes that result in the separation of particles of different sizes in nature. Depending on the field of science you belong to, this is called kinetic sieving or spontaneous stratification.

This cool video shows how sand and colored sugar separate into bands while being poured (direct link). It also talks a bit about separation of mixtures at the end.

According to Gray, Shearer and Thornton, “Kinetic sieving is so efficient in dry granular flows that in small scale experiments a layer of 100% coarse grains develops on top of a layer of 100% fines with a sharp concentration jump between them.” That is amazing!

We have assembled the apparatus shown in the video so you can also give it a try in lab.

Reference: Time-dependent solutions for particle-size segregation in shallow granular avalanches.
1. J.M.N.T Gray,
2. M Shearer and
3. A.R Thornton
Proc. R. Soc. A 8 March 2006 vol. 462 no. 2067 947-972

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