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Issue 31, 2015
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The swim force as a body force

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Abstract

Net (as opposed to random) motion of active matter results from an average swim (or propulsive) force. It is shown that the average swim force acts like a body force – an internal body force. As a result, the particle-pressure exerted on a container wall is the sum of the swim pressure [Takatori et al., Phys. Rev. Lett., 2014, 113, 028103] and the ‘weight’ of the active particles. A continuum description is possible when variations occur on scales larger than the run length of the active particles and gives a Boltzmann-like distribution from a balance of the swim force and the swim pressure. Active particles may also display ‘action at a distance’ and accumulate adjacent to (or be depleted from) a boundary without any external forces. In the momentum balance for the suspension – the mixture of active particles plus fluid – only external body forces appear.

Graphical abstract: The swim force as a body force

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Publication details

The article was received on 29 May 2015, accepted on 02 Jul 2015 and first published on 02 Jul 2015


Article type: Paper
DOI: 10.1039/C5SM01318F
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Soft Matter, 2015,11, 6235-6244
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    The swim force as a body force

    W. Yan and J. F. Brady, Soft Matter, 2015, 11, 6235
    DOI: 10.1039/C5SM01318F

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