A functional understanding of Newtons second law as a vector equation requires that students be able to reason about vectors. I present data describing students conceptual difficulties with vector addition and subtraction, and with vector quantities such as force, acceleration and tension.
These data suggest that after traditional instruction in introductory physics, some students do not recognize the vector nature of these quantities. Other students who do not have the requisite procedural knowledge to determine net force or acceleration, and are therefore unable to reason qualitatively...