Defusing Diffusion

Abstract

Diffusion has often been taught in science courses as one of the primary ways by which molecules travel, particularly within organisms. For years, classroom teachers have used the same common demonstrations to illustrate this concept (e.g., placing drops of food coloring in a beaker of water). Most of the time, the main contributor to the motion in these demonstrations is not actually diffusion, but rather convection. Yet teachers, textbooks, and workbooks continue to cite these as examples of diffusion, despite having been adequately refuted. In order to reaffirm the refutations and promote greater awareness of the continued existence of these misconceptions among teachers, the authors designed an experiment to test the premise that typical classroom diffusion experiments are, in fact, examples of convection. Taking advantage of the free-fall environment through NASA’s Teaching from Space Microgravity Experience, we were able to show that the great majority of dispersion patterns depicted in these demonstrations are due to convection. Subsequently, we propose classroom activities that serve as more accurate demonstrations of diffusion.