Our research group is developing a standardized fluids assessment, covering buoyancy and pressure. Understanding buoyancy requires a battery of skills and knowledge, and we have designed questions to probe understanding of background concepts such as density, incompressibility, and volume of fluid displaced. In this paper we will describe some of the buoyancy-related assessment questions, the misconceptions they probe, and the preliminary results from the beta version of the assessment.

While developing a standardized fluids assessment covering buoyancy and pressure, we discovered deficiencies in student understanding of density. In particular, many college students do not recognize that density is a fixed property of a solid substance, such as aluminum or gold. We added questions to our diagnostic exam to probe the extent of student difficulties. In one of our questions, only 50-60% of students (depending upon class) recognize that the density of gold is a fixed value. When similar questions from an existing diagnostic 1 are used, however, 88-100% of students correctly identify the density of a piece of wood and of a diamond as fixed values. In this paper we discuss the differences between these questions and how those differences affect student responses.