In the first step (‘‘system characterization’’), the student translates the situation to other representations,
first to a block diagram and then to a table of interactions.
The second step
(‘‘from systems to selected objects’’) guides the student in drawing a force diagram of a selected object, the
dog in this case. At this stage, the relative magnitudes of the forces that act on the object are not considered.
First, the students add force arrows to the block diagram.
The third step of the strategy considers the relative length of the arrows that represent the forces in the
force diagram. These forces can be determined based on information given in the problem or they can be
deduced from the characteristics of the object’s motion. This step enables the students to link between forces
and motion by delineating the relations between the forces and motion observed.