In this paper, a discrepant event is used to initiate a learning cycle lesson to help students develop an understanding of the concept and equation for buoyant force. The data are gathered using readily available equipment and then graphically analyzed using a four-step analysis consistent with the modeling instructional approach. This laboratory activity is appropriate for high school or first-year college physics, and provides the opportunity for review of free-body diagrams, experimental design, and graphical analysis. We use the "BSCS 5E" version of the Karplus learning cycle idea, popularized by Bybee, in which students are expected to Engage, Explore, Explain, Elaborate, and Evaluate.