  Numerous studies have demonstrated the potential for simple fluid plus
particle systems to produce complicated dynamical behavior. In this work, we
study a horizontal rotating drum filled with pure glycerol and three large,
heavy spheres. The rotation of the drum causes the spheres to cascade and
tumble and thus interact with each other. We find several different behaviors
of the spheres depending on the drum rotation rate. Simpler states include the
spheres remaining well separated, or states where two or all three of the
spheres come together and cascade together. We also see two more complex
states, where two or three of the spheres move chaotically. We characterize
these chaotic states and find that in many respects they are quite
unpredictable. This experiment serves as a simple model system to demonstrate
chaotic behavior in fluid dynamical systems.
