This paper describes how 8th grade students are using CBR, a motion detector linked to a graphing calculator, as a way of generating mathematical ideas regarding the motions concepts that surround their action. Students were previously introduced to the calculators in the classroom and teaching experiments were then carried out afterwards with a few pairs of students as a means of studying students' narratives as they faced the designed tasks. Students connected their body expressions to the Cartesian graphs generated by the motion detector. Discussion related to geometry, kinesthetic action, and functions emerged in student narratives. Data are presented based on the video-taping conducted throughout the teaching experiments and analysis developed with the help of GPIMEM, the research group. Results suggest that the use of the sensor can expand what has been labeled the epistemology of multiple representations. A theoretical view based on the notion of humans-with-media is sketched. (Contains 20 references.) (Author/ASK)