Extended Data Fig. 4: Competing effects of grain shape on bed load sediment transport.

Same as Fig. 1, but including the six granular materials in Extended Data Fig. 3. a, Comparison of bulk coefficient of static friction with a measure of grain circularity, S_c = 4πA/P², where A is the projected grain area and P is the projected perimeter (values closer to 1 indicate more-circular grains), for a compilation of observations^47,48,49 and the materials measured here. b, Comparison of the still-water-settling drag coefficient, C_Dsettle, normalized by the drag coefficient for a sphere of the same volume (Methods) with another measure of grain shape, the Corey shape factor, S_f = c/(ab)^1/2, where a, b, and c are the long, intermediate, and short axes of a grain (values closer to 1 indicate more-spherical grains), for a compilation of observations³² and the materials measured here. The coefficients of both friction and drag decrease with increasingly spherical grains. Error bars show one standard error of the mean.