Teaching the concept of free body diagrams

Free body diagrams (FBD) present a conceptual challenge for Engineering students. These diagrams are the simplest abstraction of the external forces and moments acting on a physical object. Some people “get” FBD’s the first time they are shown them while many struggle and continue to produce incorrect diagrams well into their university studies. Having received feedback from lecturers of 3rd year subjects that FBD skills were still below expectations an intervention was implemented in a University of Wollongong first year subject to (a) test students’ understanding of FBD’s (b) diagnose common misconceptions and errors and (c) reinforce the importance of constructing FBDs that are accurate and complete. This intervention has taken the form of a staged mastery skills test early in the first session of the first year of the engineering degree courses. The quiz is used as a stage gate for the subject and everyone must achieve the mastery skill to pass the subject. This paper describes some aspects of the visual learner and the design of FBD questions. Common misconceptions and mistakes are outlined with strategies for teaching the correct approach. Finally some correlations are given between performance in the skills test and subsequent performance in engineering mechanics subjects.