What Have We Learned About Friction Since Coulomb?
Seminars of the Institut de Physique de Nice,
Abstract:
Friction responsible for an estimated 23% or the world energy consumption. It is one of the oldest problems in physics — first codified by Amontons and Coulomb in the 17th and 18th centuries — yet its microscopic origin remains a topic of intense research. I will discuss our recent work, where we developed techniques to visualize and quantify what Coulomb could only infer: the real area of contact between rough surfaces. By combining fluorescence microscopy techniques with molecular rigidochromic and mechanophore sensors that light up under confinement and under stress, we have mapped frictional contacts down to their nanometer-scale structure and local shear strength. In connecting these observations to contact mechanics and molecular-scale physics, we are beginning to transform Coulomb’s empirical law into a quantitative, predictive framework — one that unites materials physics and mechanics, across scales, from single asperities to sliding interfaces.
Taking ciliated green algae as a paradigmatic example, here I will discuss our current understanding of the importance of both hydrodynamics and direct mechanical coupling in flagellar synchronisation. I will then present the results of new experiments which allow us to selectively block hydrodynamic coupling between the flagella of a single cell and therefore probe directly the role of hydrodynamics in their synchronisation. These results reveal a link between the type of coupling and the resulting synchronisation state, and suggest a previously unrecognised mechanism by which flagella can sense mechanical stimuli
