*50%*:**Students' difficulties with unit vectors and scalar multiplication of a vector***41%*:**A research-based approach to improving student understanding of the vector nature of kinematical concepts***39%*:**Investigation of Student Difficulties with Graphical Representations in Physics***39%*:**An Investigation of Student Understanding of Basic Concepts in Special Relativity***38%*:**University students' conceptions of basic astronomy concepts***38%*:**Student Preconceptions about Vector Kinematics***38%*:**Students' Difficulties in Interpreting the Torque Vector in a Physical Situation***38%*:**Testing Students’ Understanding of Vector Concepts***38%*:**Students' Conceptions About the Vector Characteristics of Three Physics Concepts***38%*:**An investigation of students' abilities in establishing relations between some physical concepts***38%*:**Improving students’ understanding of quantum measurement. I. Investigation of difficulties***37%*:**Student difficulties with concepts related to entropy, heat engines and the Carnot cycle***37%*:**Students’ Understanding of the Concepts of Vector Components and Vector Products***37%*:**Test of understanding of vectors: A reliable multiple-choice vector concept test***37%*:**Conceptual Understanding of Quantum Mechanics: An Investigation into Physics Students’ Depictions of the Basic Concepts of Quantum Mechanics***36%*:**Initial understanding of vector concepts among students in introductory physics courses***35%*:**Development of a concept inventory to assess students' understanding and reasoning difficulties about the properties and formation of stars***34%*:**Student Difficulties with Wave Concepts***34%*:**Investigation of student understanding of the concept of velocity in one dimension**