HOW DO STUDENTS USE SPATIAL REASONING TO MAKE SENSE OF DEMONSTRATIONS IN DENSITY TANKS?

We used density tanks to investigate student use of spatial reasoning while making sense of fluid behavior. Density tanks can be a teaching tool in meteorology and oceanography classes for modeling fundamental concepts that emphasize how fluids of different densities behave when combined. A density tank is a rectangular tank with a removable dividing wall. Density tanks can model fluid stratification, weather fronts, ocean overturning circulation, and internal waves. Differences in water density occur due to variations in temperature, salinity, or both. During our investigation with students, we used food color to make apparent these differences while demonstrating interactions of water of different densities immediately and through time. Our pilot work showed that students struggle to make sense of basic demonstrations, so we began with simple models of water mixing. We worked with 26 students in individual semi-structured, interviews with students predicting what could happen when contrasting colored waters of different densities interact. We combined think-aloud methods with sketching and interactive discussion to prompt student thinking, encourage sense-making, and make spatial reasoning processes visible. We video-recorded and transcribed each session and collected predictive and post sketches. To analyze the data, we used an inductive and comparative method that sought to characterize student spatial reasoning. Our findings suggest that students generally form initial conceptions of density from memories related to food, experiences in the ocean, or early science education. Students had little preconceptions of salt diffusion or heat transfer in water. Students were typically surprised at the initial interactions of the water upon removing the dividing wall and after a minute to an hour. Our work is addressing questions such as “Do misconceptions originate with fluid behavior, heat transfer, or both?” “Do students reason about density related to temperature differently than density related to salinity?” and “On what experiences are students basing their predictions?” These results precede potential inquiries into how students make the conceptual leap between abstract ideas and observable fluid behavior, and how instructors can best use these demonstrations in fluid-Earth science courses.