Fluid Dynamics in Elementary School

My younger son is taking an elective in Aerodynamics, and I volunteered to do a fluid mechanics demo next week. The subject is air resistance, and I am going to try to make a visualization of the whorls and eddies behind a moving object by floating talcum powder on top of water. I vaguely remember seeing this in college but I haven't tried it yet. I tend to leave things to the last minute, but I had better try this out later today to see if it really works...