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. 2019 Mar 11;9:4095. doi: 10.1038/s41598-019-40797-y

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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(a) Collapse of data from a circular slider of radius R = 4.00 ± 0.05 mm and mass m = 61 ± 2 mg, and two elliptical sliders with the same surface area. One elliptical slider slid with its major semi-axis a = 5.00 ± 0.05 mm parallel to the direction of motion and has mass m = 57 ± 2 mg, while the other slid with it minor semi-axis a = 3.20 ± 0.05 mm parallel to the direction of motion and has mass m = 54 ± 2 mg. b denotes the semi-axis perpendicular to the direction of motion. (b) Comparison of data from circular sliders with and without a grooved bottom. Sliders with ridges parallel to the direction of motion experience less friction than a slider without ridges or with ridges perpendicular to the direction of motion. Friction decreases further by increasing the spacing between the ridges. Sliders were all of radius R = 4.00 ± 0.05 mm and the masses were in the range m = 76–86 mg with uncertainty 2 mg.