The authors of this Hot paper model a steel ball falling freely through a solution of entangled wormlike-micelles. In non-Newtonian fluids such as this, objects are known to settle unsteadily. They report for the first time that spheres larger than a critical size undergo unsteady motion and show sustained, repeated bursts of oscillations superposed on a constant baseline velocity.
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Oscillatory settling in wormlike-micelle solutions: bursts and a long time scale
Nitin Kumar, Sayantan Majumdar, Aditya Sood, Rama Govindarajan, Sriram Ramaswamy and A. K. Sood
Soft Matter, 2012, 8, 4310-4313, DOI: 10.1039/C2SM25077B