W. G. Pritchard Lab Seminar - 109 Boucke Building

	     **November 7, 2001**
	
Studies of Wetting and Drag Force in Granular Media.

Peter Schiffer

Department of Physics
Penn State University

Abstract:

In the last decade, condensed matter physicists have begun an intense
study of the dynamic and static properties of granular media (materials
made from individual macroscopic solid grains).  I will discuss recent
work on two different physical phenomena in granular media which are
familiar to the beach goer but are only just beginning to be examined
by physicists:  1) How interstitial liquid between the grains affects
granular properties and leads to the development of correlations between 
the grains.  Our recent experiments have shown that interstitial liquid 
results in a variety of unexpected behavior, including the formation of 
correlated, a non-monotonic change in the angle of repose with 
increasing liquid content, and spontaneous pattern formation in the 
granular surface; 2) How the motion of an object being pulled slowly 
through a granular medium is resisted by the grains, resulting in a drag 
force which differs dramatically from viscous drag in a fluid, both in 
its average properties and in having large fluctuations with distinct 
characteristics.  The fluctuations and dependence of the drag force on 
depth in the medium, size and shape of the object, grain size and 
velocity have all been studied experimentally.