Using the System Schema Representational Tool to Promote Student   Understanding of Newton's Third Law
  The Modeling Instruction program at Arizona State University has developed a representational tool, called a system schema, to help students make a first level of abstraction of an actual physical situation [1]. A system schema consists of identifying and labeling all objects of interest from a given physical situation, as well as all the different types of interactions between the objects. Given all the relevant objects and their interactions, students can explicitly identify which are part of their system and which are not, and then go on to model the interactions affecting their choice of system as either (i) mechanisms for energy transfer, or (ii) forces being exerted. In this paper, I describe the system schema tool, give examples of its use in the context of forces, and present some evidence on its effectiveness in helping students understand Newton's Third Law. 
Brant E. Hinrichs