The acquisition metaphor of learning is often used by teachers of physics: Students are thought to acquire a particular concept and then transfer this concept to new contexts. For example, one might argue that students acquire the mathematical concept of "vector addition" and then apply it in different physical contexts. In this study, 200 freshmen taking an introductory physics course were asked to calculate total force, total displacement and total momentum in simple contexts involving vector addition at right angles. Another similar group of students were asked to calculate net force, net displacement, and net momentum. When asked to calculate the "net" quantity, students did significantly better than when asked to calculate the "total" quantity. Students did significantly worse when adding momenta as opposed to adding forces or displacements. These results are inconsistent with a basic "acquisition–transfer" perspective of learning. An analysis of subsequent interviews and questionnaires was also conducted.