In this paper, we provide a detailed discussion about the development of a new concept inventory that is
designed to assess student understanding of Newtonian gravity in general education introductory college
astronomy courses, hereafter “Astro 101.” The Newtonian Gravity Concept Inventory (NGCI) probes several of
the common student conceptual and reasoning difficulties with the concept of gravity as described in the
literature (Ameh 1987; Smith and Treagust 1988; Sharma et al. 2004; Dostal 2005; Kavanagh and Sneider
2006–2007a and 2006–2007b; Feeley 2007; Asghar and Libarkin 2010; Williamson and Willoughby 2012).
Specifically, the concept mapping, phenomenographic analysis of student-supplied responses to open-response
questionnaires, and characterization of students’ mental models described in our previous paper, Williamson and
Willoughby (2012), guided the conceptual focus and item construction of the NGCI. This foundational work
represents the Planning phase of the instrument development model of Benson and Clark (1982).