Pollution against the stream

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Particles can flow up the water flow when preparing mate tea .

Counter-current pollution by floating particles is a paradoxical phenomenon in fluid dynamics : when water flows from a higher container into a lower one, dirt particles from the lower container can swim upstream into the upper container.

The phenomenon is still being investigated. Experiments and computational analysis suggest that it can be mainly explained by surface tension differences . However, eddies also have an influence that has yet to be checked.


Experimental setup to generate a constant flow from the upper to the lower container.

The phenomenon was first observed in 2008 by the Argentinian Sebastian Bianchini at the University of Havana while making mate tea . Together with Alejandro Lage-Castellanos he carried out a series of experiments . Ernesto Altshuler later joined them in Havana . The investigations resulted in Bianchini's thesis and a short publication in arxiv . The phenomenon was presented as a surprising fact in some online magazines from 2011. Videos showing the effect are available on YouTube .

Bianchini's thesis showed that the phenomenon can be reproduced in the laboratory using mate sheets or chalk powder as dirt particles. The work also showed that temperature gradients between the containers (hot at the top, cold at the bottom) are not necessary to create the effect. This research also showed that surface tension plays an important role in explaining the so-called Marangoni effect , which was suggested by two observations: (a) the chalk powder and mate sheets reduced the surface tension in the lower container and (b) as soon as industrial surfactants , which were added to the upper container, the particles stopped floating against the current into the upper container.


After a lecture by Alejandro Lage-Castellanos on the physics of complex matter in Havana (MarchCOMeeting, 2012) Troy Shinbrot ( Rutgers University ) became interested in the topic. Together with the student Theo Siu, the results of the earlier studies were confirmed and expanded with new experiments and numerical simulations at Rutgers University, which led to a joint work.

The results were later confirmed independently by others. It remains to be seen whether the phenomenon is caused solely by differences in surface tension or also depends on the dynamic behavior of the flowing water.


The counter-current contamination phenomenon could be relevant for industrial and biotechnological processes.

Individual evidence

  1. ^ A b S. Bianchini, A. Lage-Castellanos, E. Altshuler: Upstream contamination in water pouring. arXiv : 1105.2585 , 2011.
  2. ^ Contaminants Can Flow Up Waterfalls, Say Physicists. 2011, accessed July 13, 2020 .
  3. Veronique Greenwood: Small Particles Can Flow Up Waterfalls, Say Tea-Drinking Physicists. In: Discover Magazine . May 17, 2011, accessed July 11, 2020 .
  4. ^ Bob Yirka: Some particles are able to flow up small waterfalls, physicists show. In: PhysOrg.com. May 18, 2011, accessed July 11, 2020 .
  5. ^ Andrew Grant: Particles defy gravity, float upstream. In: ScienceNews. July 2, 2013, accessed July 11, 2020 .
  6. Upstream contamination in water pouring on YouTube (A. Lage-Castellanos, 2013).
  7. Upstream Contamination by Floating Particles on YouTube (2014).
  8. a b Bianchini S. et al .: Upstream contamination by floating particles . In: Proceedings of the Royal Society A . tape 469 , no. 2157 , 2013, p. 20130067 , doi : 10.1098 / rspa.2013.0067 , bibcode : 2013RSPSA.46930067B .
  9. Upstream Contamination by Floating Particles on YouTube (2014).