Gas Diffusion - Model
To model the diffusion of gas molecules through a small hole.
White ping pong balls on one side and colored ping pong balls on the other side of a plastic sheet barrier are agitated by a motor which rotates the bottom of the model. Opening a small hole in the plastic barrier between the two sections allows some of the balls to "diffuse" from one side to the other.
Roger A. Key and B. D. DePaola, Apparatus for Teaching Physics: A Simple Apparatus for Demonstration of Gaseous Diffusion, TPT 29, 522-523 (1991).