Friction affects many aspects of everyday life and has played a central role in technology dating from the creation of fire by rubbing sticks together to current efforts to make nanodevices with moving parts. The friction "laws" we teach today date from empirical relationships observed by da Vinci and Amontons centuries ago. However, understanding the microscopic origins of these laws remains a challenge. Friction is a complex multiscale phenomenon that depends on both atomic interactions in contacts, and the macroscopic elastic and plastic deformation that determine the morphology and stress distribution within these contacts. Recent experiments and simulations have provided new information about friction at the atomic scale. The results are often counterintuitive, with solids sliding more easily than fluids and fluids resisting shear like solids. The talk will discuss the origins of friction, starting with how roughness affects the area where two surfaces actually touch, and then considering how surfaces can lock together in regions of contact to produce the macroscopic friction laws we teach. Selected References: G. He, M. H. Muser and M. O. Robbins, Science 284, 1650 (1999). M. H. Muser, M. Urbakh, and M. O. Robbins, Advances in Chemical Physics 126,187 (2003). J. Ringlein and M. O. Robbins, Am. J. Phys. 72, 884 (2004). S. Hyun, L. Pei, J.-F. Molinari and M. O. Robbins, Phys. Rev. E70, 026117 (2004). B. Luan and M. O. Robbins, Nature 435, 929 (2005). C. Campana and M. H. Muser and M. O. Robbins, J Phys.: Condens. Matter 20, 354013 (2008).
Coffee and cookies before the presentation at 3:15 pm, and refreshments after the presentation will both be served in Room 128.