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Fluid dynamics

That sinking feeling

Nature volume 409, pages 569–571 (2001)Cite this article

The physics of slowly falling particles in a fluid remains surprisingly enigmatic. Luckily, laws that work for dilute suspensions also appear to apply to higher — and more useful — particle concentrations.

Particles moving through a viscous fluid interact with each other, because each individual particle drags fluid along with it, which then drags on other particles. These hydrodynamic interactions are important in many processes, from the deposition of silt in a river to the motion of dust in the air and the centrifugation of proteins. But despite a century of research, the character of these motions is still hotly debated, even for dilute suspensions in which the particles are well separated. On page 594 of this issue, Segrè et al.1 provide experimental evidence that the laws governing particles settling under gravity at high concentrations are quantitatively similar to those at very low concentrations. This result is unexpected, because it has long been assumed that particle motion in a dense suspension is qualitatively different from the dilute case.

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Figure 1: The physical mechanism underlying velocity fluctuations of particles in a sediment.

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Authors and Affiliations

  1. Department of Mathematics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, 02139-4307, Massachusetts, USA

    Michael P. Brenner & Peter J. Mucha

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  1. Michael P. Brenner
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  2. Peter J. Mucha
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Correspondence to Michael P. Brenner or Peter J. Mucha.

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Brenner, M., Mucha, P. That sinking feeling. Nature 409, 569–571 (2001). https://doi.org/10.1038/35054641

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