We are interested in studying the cell/microcarrier motions within the NASA rotating bioreactor system, with the eventual goal of using this description to understand the attachment of cells on microcarriers and the assembly of these cell/bead constructs into three dimensional tissue. In this study, we used both experimental imaging tools and numerical analysis to study the motions of typical microcarrier beads used in the High Aspect Ratio Vessel (HARV). Experimental studies demonstrate that physical properties of the microcarrier beads affect directly the primary radial motion of these particles, and also show that these beads interact and aggregate with each other over time. Numerical analyses using the appropriate governing equations and a Runga-Kutta solution method show that computed results agree with experimental observations on both primary and secondary particle trajectories. From the numerical analysis, we develop an analytical description of a typical particle trajectory in the laboratory frame and develop an experimental apparatus to track a single particle temporally in the bioreactor. Results from this study provide insight into the motion and aggregation of particles in the rotary culture bioreactors over time, and can lead to a better control of the bioreactor mechanical environment.