Free-Response Questionnaires
We chose a ten-item free-response format as the best method to probe introductory astronomy student understanding of gravity.
This serves three purposes: (1) to explore different representations of gravity in a variety of situations, (2) to allow for analysis via a constant comparative method, as discussed below, and (3) to gain information for distracter responses for a multiple-choice test that represent typical student answers in their typical language.
In keeping with our goal of focusing on the causes, effects, and extent of gravity, the questions had little to no emphasis on equations.
In order to reliably measure a student’s mental model, we avoided questions
where students needed to have heard the answer before, instead emphasizing questions whose answers can be deduced easily by a true understanding of gravity.
These are generally different types of questions than those that are asked in textbooks at the end of the chapter.
The questions explore the strength of gravity in a variety of environments and contexts—on the moon, in space, in freefall, on planets with orbiting bodies, etc.
In total, 30 questions were developed for the questionnaires, and these questions were divided evenly into three versions: A, B, and C
(see Appendix A for a compilation of the questions that were used for this paper).
Eachsection of introductory astronomy in the Fall semester of 2010 was given 30 minutes to complete a different version of the questionnaire.
Half of the questions in each version of the questionnaire were composed in text
only, and the other half provided a figure of the situation described in the question.