Students' difficulties in interpreting the torque vector in a physical situation

In this article we investigate students' difficulties in interpreting the torque vector in a physical situation. To identify these difficulties, we carried out task-based interviews with undergraduate physics majors completing a junior level course in mechanics. In the task, we presented a drawing of a beam that is initially at equilibrium over a fulcrum. Later, a weight is hung from the left side. We detected an alternative conception in which students thought that the left side of the beam and the weight would have additional motion in the direction of the torque vector. To quantify students having this alternative conception, we designed and administered a multiple-choice question to undergraduate physics majors completing a sophomore-level modern physics course. We found that 18% of the students had this conception. Based on these results, we present some suggestions for instruction of the torque vector concept.