Rotations from a New Perspective: Experiments, Modelling and Analogies Based on Angular Momentum as an Extensive Quantity

Concepts and mathematical instruments used in elementary mechanics are often perceived as abstract entities by students. We propose therefore an approach to the description of rotational mechanical processes based on a conceptualization of angular momentum grounded on image schemes and analogies from common everyday experience (Fuchs, 2007). In our approach angular momentum is described as a conserved extensive quantity, whose balance equation is either an instrument to foster clear mental images of rotational processes, or a solid base for algebraic development. Exploiting analogies, in this work we show how this way angular momentum can be stored in rotating bodies, how their moment of inertia represents their angular momentum capacities, and finally how a torque applied to a rotating body can be imagined as an angular momentum flow. We analyse from this point of view three experiments, using on-line data acquisition and dynamical modelling. The use of analogies allows indeed to develop dynamical models in a wide range of contexts, able to strengthen basic concepts and discuss phenomena in relation with the initial conditions and the parameter values.