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Seminar: Wednesday, Oct. 10, 2012 at 3:30 pm

From Random Walks to Brownian Motion to Diffusion and Entropy:
Statistical Principles in Introductory Physics
Mark Reeves
Department of Physics George Washington University

Introductory biology courses often begin with an exploration of the qualities of water that are important to living systems. One idea that is often not addressed is dominant contribution of the entropy of water molecules in driving biologically important processes towards equilibrium. Compounding the problem, many introductory physics courses have deemphasized entropy, almost to the point of eliminating it entirely. In contrast, we are teaching this concept in our introductory physics and biology classes, and are collaborating to bring the pedagogical approaches of Scale-Up Physics teaching into biology instruction. From a content point of view, we strive to bring quantitative modeling into the biology class and life into the physics course. To this end, students are introduced to prediction and random walk by first considering coin flips. We move on to a Java-based simulation of the random walk problem that mimics the diffusion of molecules in water. The simulations are complemented by lab experiments in which Brownian motion and dye diffusion in agarose gels are observed and quantitatively measured using ImageJ software. These measurements link the microscopic model of Brownian motion to its macroscopic realization in diffusion. Furthermore, this curricular unit, which is presented in both the introductory physics and biology classes, leads to the important conclusion that lipid bilayers and folded proteins are formed because of the entropic release of water molecules from the surfaces of hydrophobic moieties. Formative and summative assessments of the students’ learning provide perspectives to the challenges of our joint curricular reforms.

Location: Physics Bldg., Room 401