2024 ASEE Annual Conference & Exposition

After defining a system for analysis, a rigorous process is taught to students in their Statics and
Dynamics courses on how to draw proper kinetic, free-body, and impulse-momentum diagrams.
While numerous techniques and mnemonics have been mentioned in literature, any experienced
instructor can tell a correct free-body diagram apart from an incorrect one. Unfortunately, this is
not the case when considering scalar properties such as mass, energy, exergy, and entropy.
Different fluid mechanics and thermodynamics texts have treated the diagrammatic representation
of these properties either very poorly, or in the case of the latter two, not at all. In this paper, the interaction diagram is introduced as a graphical tool to represent the aforementioned scalar properties. The interaction diagram combines the conservation and accounting of properties with the template of the kinetic, free-body, and impulse-momentum diagrams. Three examples are provided to show the application of this general diagrammatic approach to different types of problems that involve the change in multiple properties. The impact of incorporating interaction diagrams when introducing conservation and accounting principles involving scalar properties is assessed through the evaluation of student performance on exams and student feedback.