Pendulums,Pedagogy, and Matter: Lessons from the Editing of Newton's Principia

Teaching Newtonian physics involves the replacementof students' ideas about physical situations with precise conceptsappropriate for mathematical applications. This paper focuses on theconcepts of `matter' and `mass'. We suggest that students, likesome pre-Newtonian scientists we examine, use these terms in a waythat conflicts with their Newtonian meaning. Specifically, `matter'and `mass' indicate to them the sorts of things that are tangible,bulky, and take up space. In Newtonian mechanics, however, the termsare defined by Newton's Second Law: `mass' is simply a measure ofthe acceleration generated by an impressed force. We examine therelationship between these conceptions as it was discussed by Newtonand his editor, Roger Cotes, when analyzing a series of pendulumexperiments. We suggest that these experiments, as well as moresophisticated computer simulations, can be used in the classroom tosufficiently differentiate the colloquial and precise meaning of theseterms.