Student use of vectors in introductory mechanics

Most students' initial exposure to physics is in the context of kinematics and dynamics. An understanding of how these topics relate to each other requires the ability to reason about vectors that represent forces and kinematic quantities. We present data that suggest that after traditional instruction in mechanics many students lack this ability. Modifications to instruction can significantly improve student performance on questions about vector addition and subtraction and increase the likelihood that students employ vectors in their attempt to solve mechanics problems. However, an increased emphasis on these topics has so far been only moderately successful in promoting the level of proficiency required to understand the connection between force and acceleration as vector quantities. We describe some of the procedural and reasoning difficulties we have observed in students' use of vectors. (C) 2004 American Association of Physics Teachers.