2019 ASEE Annual Conference & Exposition

Drawing a good free-body diagram (FBD) is generally acknowledged by mechanics instructors as a critical step in solving mechanics problems. In this paper we will summarize recommended procedures and mnemonics that have been developed to help students draw good FBDs. In spite of the fact that every Statics book we examined presented a step-by-step procedure for drawing free-body diagrams, they all included what the authors consider to be poor practices that can lead to misconceptions and difficulties when students take Dynamics. We will discuss these pitfalls in Statics textbooks, show examples from popular Statics textbooks that illustrate them, and discuss how the consistent use of effective FBD drawing strategies can be used to avoid them. We surveyed experienced instructors who use free-body diagrams and asked them to rate, in their opinion, the importance of each element of a FBD we identified from the procedures presented in Statics books, and we also asked them to choose between two mnemonics for drawing FBDs: “The ABC’s of FBD’s” and “BREAD.” We found that, in general, faculty members agreed on most of the elements, although there was no consensus on the importance of including dimensions on a FBD. Of the mnemonics, 57% of the respondents preferred “BREAD,” 24% preferred “The ABC’s of FBD’s,” and 19% had no preference.