Multiple-choice Concept Inventories (CIs) have become important tools in the Astronomy Education Research
community for assessing student learning and the effects of instructional interventions. CIs focus on a narrow
domain of topics that are central or foundational to the overall Astro 101 curriculum (Bailey 2009). The
multiple-choice questions used in a Concept Inventory endeavor to model students’ natural language, minimize
scientific jargon, and provide research-based distractor choices that represent common student naıve beliefs and
reasoning difficulties. There are currently other CIs for Astro 101 courses that measure student understanding
about lunar phases (Lindell and Olsen 2002), star properties (Bailey 2006), the green house effect (Keller 2006),
light and spectroscopy (Bardar et al. 2007), and the solar system (Hornstein et al. 2011). In addition to these
topics, the topic of Newtonian gravity is a foundational topic for Astro 101. An understanding of gravity
enhances students’ ability to solve problems and reason about the motion of bodies in space, the formation of
planets and stars, and the large-scale structure of the universe. To quickly and reliably probe Astro 101 students’
understanding of this important topic, and to provide a useful tool for faculty to assess success in their classes,
we have developed the Newtonian Gravity Concept Inventory (NGCI).