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Accueil du site > Évènements > Séminaires > Séminaires Fédération > Archives Fédération > 2014

Lundi 3 Novembre 2014 / FPeiresc

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Séminaire Fédération

Orateur : Daniel Bonn

Institut of Physics, University of d’Amsterdam

Titre : "How did the Egyptians build the pyramids ? Mechanics of and sliding friction on wet sand"

Date et lieu : le Lundi 3 Novembre à 14h, IUSTI.

Résumé : I will discuss the rheology and mechanical properties of wet granular materials, and show why the behavior can be very subtle. Once one understands the mechanical properties, I will show that one can use this knowledge to construct the perfect sandcastle, or to understand why the ancient Egyptians wetted the desert sand with water before sliding heavy stones over it (Figure). I will then go on to show some new results on friction at the microscopic scale, between 2 grains. Amonton’s famous friction law states that the friction force is proportional to the normal force since both are proportional to the area of contact. However for spherical grains, the contact area is not proportional to the normal force, as shown by Hertz long ago. We use a new fluorescence technique that allows us to probe the real area of contact between 2 rough surfaces. In our case, we conclude that both Amonton and Hertz were right, but apply on different length scales.