A numerical simulation of a particle in a horizontal pipe has been carried out, and the variation of aerodynamic forces is described. The major forces that control particle motion are drag in the axial direction, and lift due to air velocity gradient and due to spin in the transverse direction. An elastic contact model based on rigid body sliding has been incorporated, which avoids particle settlement without having to use any form of irregular bounce. The results from the simulation agree closely with experimental time-of-flight measurements. (c) 2005 Elsevier B.V All rights reserved.