  Mastering problem solving requires students to not only understand and apply
physics concepts but also employ mathematics and mathematical representations
(sketches, diagrams, graphs, gestures, equations and spoken language)
skillfully. As part of a larger project to investigate problem solving
processes among upper division physics students, we investigate how students
coordinate among multiple representations while solving problems. Data for this
study is drawn from an upper-division Electromagnetism I course, where students
engage in individual oral exams. We do moment-by-moment analysis of students'
problem solving to see how they translate between durable representations
(diagrams, written mathematical equations) with the help of evanescent
representations (gestures, words); and how they build up durable
representations where they can "stand fast" later. In this paper, we present
the case of Larry as an exemplary case for problem solving. Larry starts from a
durable representation (diagram) and builds up from there using evanescent
representations (gestures and words), standing fast on the diagram. He later
translates to a different kind of durable representation (mathematics), where
he reasons and answers the original problem.
