What College Students Don't Know about Density

As part of the development of a fluid statics assessment, our research group conducted clinical interviews with students in both conceptual physics and calculus-based introductory physics courses. What were intended as ``basic'' questions about density quickly became a significant focus of those interviews, as only one of the eight students interviewed demonstrated a confident understanding of mass density. Questions have since been added to the fluid assessment to probe the prevalence of these difficulties. In this talk, I will summarize our preliminary data and discuss future plans for the assessment and our instruction.