Feet used for powerful swimming: true frogs
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The webbed back feet of true frogs are used to swim by pushing back against the water creating vortex rings.
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"The wake showed two vortex rings left behind by the two feet. The rings appeared to be elliptic in planform, urging for correction of the observed ring radii. The rings’ long and short axes (average ratio 1.75:1) were about the same size as the length and width of the propelling frog foot and the ellipsoid mass of water accelerated with it. Average thrust forces were derived from the vortex rings, assuming all propulsive energy to be compiled in the rings. The calculated average forces (Fav=0.10±0.04·N) were in close agreement with our parallel study applying a momentum–impulse approach to water displacements during the leg extension phase.
"We did not find any support for previously assumed propulsion enhancement mechanisms. The feet do not clap together at the end of the power stroke and no ‘wedgeaction’ jetting is observed. Each foot accelerates its own water mantle, ending up in a separate vortex ring without interference by the other leg." (Stamhuis and Nauwelaerts 2005:1445)
edible frogRana esculenta Linnaeus, 1758
IUCN Red List Status: Least Concern
Habitat(s): Wetlands
Natural History Information: Also called Pelophylax esculentus.
Some organism data provided by: ITIS: The Integrated Taxonomic Information System
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist
Application Ideas: Flexible appendages for ships, planes, or boats that can be used to increase or decrease drag as needed; flexible stabilizing attachments for marine infrastructure; flexible fabrics for safety equipment.
Industrial Sector(s) interested in this strategy: Transportation, shipping, marine siting, textiles
Foy, Sally; Oxford Scientific Films. 1982. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London. 238 p.
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Stamhuis, E. J.; Nauwelaerts, S. 2005. Propulsive force calculations in swimming frogs II. Application of a vortex ring model to DPIV data. Journal of Experimental Biology. 208: 1445-1451.
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Nauwelaerts, S.; Stamhuis, E.J.; Aerts, P. 2005. Propulsive force calculations in swimming frogs I. A momentum–impulse approach. Journal of Experimental Biology. 208: 1435-1443.
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