Different characteristics of the motion of a single particle on a bumpy inclined line

(Received 18 January 1994, revised 24 March 1994, accepted 15 April 1994)

Abstract
In order to better understand the yole of friction and disorder in segregation mechanism in surface flow, we investigate the motion of a single ball of radius R on a onedimensional bumpy line made of balls of radius r. The smoothness is then controlled by R/r, the ratio of radii. In addition to experimental results for different ratios, we perform numerical simulations where the bumpiness - disorder in spacing between the balls forming the line - is also controlled. Different kinds of behavior are observed. In particular, we obtain a regime where the ball quickly reaches a constant mean velocity. In this regime, we investigate the friction forces during contacts and identify in a generalized model the regions which are dominated by solid friction or by loss due to collisions. We show that smaller balls get trapped more easily on a rough surface which might explain the origin of the segregation process found in rotating drums and sandpiles. We also study this system for different values of the bumpiness of the line and find conditions under which the constant velocity regime disappears completely.