In this paper a class of regular surfaces, generated by rotation and twist of a rigid line segment, is considered. Firstly a complete description of those surfaces by means of local charts is obtained and then its orientability is characterized in terms of the number of half-twists, taking into account their direction (clockwise or…

Reports on a small-scale investigation of student understanding of moments of forces to provide some indication as to the nature of intuitive ideas in this area. Results of the investigation suggest three stumbling blocks in the conceptual understanding of moment of forces. (Author/ASK)