Ponencia presentada en el XIX Congreso Internacional de Acústica (ICA2007), Madrid, 2-7 Sep 2007.-- PACS: 43.55.Cs.This paper presents a numerical study of nonlinear drift motions experienced by small particles in a plane standing wave. A single half-wavelength resonator is considered for the study. Ignoring Brownian motion, components of the forces acting on a particle are considered along the acoustic field direction and perpendicular to it, taking into account the gravity. The Primary radiation force, due to nonlinear interactions between the incident and particle scattered waves governs the particle motion from any location toward the node of acoustic pressure, in the middle of the resonator. Other second-order nonlinear interactions due to the acoustic wave effect and the mutual radiation pressure are also included in this study. These mechanisms generate forces on the particles much weaker than the radiation force with a shorter range of applicability concerning to distances up to various orders of magnitude higher than the particle radii.In this way, the particle motion near the node of pressure can be slightly affected by the secondary nonlinear mechanisms, producing certain deviations of their trajectories around their locations of equilibrium. Also the drift motion of smaller particles in polydisperse suspensions of differently sizes can be altered by the influence of other bigger particles close to them.Peer reviewed