BOX 6.2 How Do You Know? A 1-kilogram stick that is 2 meters long is placed on a frictionless surface and is free to rotate about a vertical pivot through one end. A 50-gram lump of putty is attached 80 centimeters from the pivot. Which of the following principles would allow you to determine the magnitude of the net force between the stick and the putty when the angular velocity of the system is 3 radians/second? A. Newton's second law, B. Angular momentum or conservation of angular momentum C. Linear momentum or conservation of linear momentum D. Work-energy theorem or conservation of mechanical energy E. Conservation of linear momentum followed by conservation of mechanical energy Performance on this item was near random for students finishing an introductory calculus-based physics course. The temptation is to match the "rotation" surface feature of the problem with "angular momentum," when in fact the problem is solved by a simple application of Newton's second law. Data such as these are important for helping teachers guide students toward the development of fluid, transferable knowledge (Leonard et al., 1996).