Solid friction reduction on the skin of the sandskink
Sandskink (Scincus scinus) |
Ingo Rechenberg & Abdullah Regabi El KhyariHypothesis of the BionicistsSwimming in the sand under a dune, demonstrated by the sandskink of the Sahara, is certainly much more exhausting than swimming in the water. Therefore, if energy reduction is the main objective of biological evolution, the scales of the sandskink should have a mechanism to reduce the solid friction. Really, the surface of a sandskink looks highly polished. |
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Experiments in the desert Erg Chebbi (Morocco)In the summer 2000 we* measured in the Sahara for the first time the sand friction coefficient on the surface of the sandskink. The idea for the construction of a dynamic friction meter was the principle of an hour glass. Out of the cannula of the glass vessel a sand stream is flowing down to the inclined test surface |
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Definition and measuring of the dynamic friction coefficient μ |
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If the inclination angle of the test surface isn't too small the sand is flowing on. The tangent of the angle for which the sand stream stops is called the dynamic friction coefficient. For narcotizised and for killed sandskinks we obtained a sand gliding angle of 21°. When we repeated the experiment in the sommer 2002 we obtained for an absolutely undamaged animal even a critical angle of 19°. |
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20°
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22°
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Surface comparisionParallelly to the above experiments we measured the critical sand sliding angle for some technical materials. The results: polished steel = 25° glass = 28° nylon = 30°.
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Sand friction on the surface of the sandfisch compared with the friction on other materials |
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Quintessence of the experiments: Biological evolution has worked out a solution with minimum solid friction. The technical imitation of the skink surface gives the chance to develop a new generation of sliding-bearing materials. For instance: Disciples of the sport of sand-boarding may use it. |
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Sand Boarding