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. 2010 Feb 10;6(3):398–401. doi: 10.1098/rsbl.2009.1041

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© 2010 The Royal Society

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Figure 2. — Model of locomotion on sand: (a) flipper ground reaction force F_thrust and inertial force ma. (b) Drag force versus displacement shows rapid rise in force (the yield force F_yield) for small initial displacement. Inset: quadratic dependence of F_yield on insertion depth d. The bar shows range of measured flipper depths. (c) Normalized turtle inertial force (ma/F_yield) versus limb frequency (fit curve is ma/F_yield = cfⁿ; c = 0.21, n = 1.74, r² = 0.65). Dashed line indicates predicted yielding threshold for a single flipper inserted to average measured turtle depth (grey region is yield for mean ± s.d. depth).