What Makes Things Float? Density and Buoyancy Misconceptions. Esther Dabagyan. California State University Northridge

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1 What Makes Things Float? 1 Running head: WHAT MAKES THINGS FLOAT? What Makes Things Float? Density and Buoyancy Misconceptions Esther Dabagyan California State University Northridge

2 What Makes Things Float? 2 WHAT MAKES THINGS FLOAT? Density and Buoyancy Misconceptions There are many deep and basic misconceptions that contribute to confusion regarding why objects sink and float. This being my second year teaching a density immersion unit that allows students to develop their own concept of density and buoyancy though inquiry and investigation, I am very curious as to what ingrained knowledge students may bring with them into the classroom regarding this topic. Density is typically regarded as a higher order concept (Kohn, 1993, p. 1637); by this I mean that some cognitive theorists such as Jean Piaget would claim that it is beyond the capability of children under the age of 9 to fully grasp it due to developmental issues (as cited in Kohn, 1993, p. 1637). Both the limitation of age and simple misconceptions that people of all ages have will be explored in this paper. The word misconception will be used in this paper according to disessa s definition, as fragmented pieces of knowledge gained through experience (as cited in Hardy, Jonen, Moller, & Stern, 2006, p. 308). Developmental misconceptions in young children up to age nine seem to largely center on two ideas. The first is the confusion between weight and volume (Piaget, 1930, p. 165). Many students experience the inability to explain volume without referring to weight. When children are asked to explain why a larger item displaces more water than a smaller item, they often persist that it is due to the item s weight, not volume. According to Piaget (1930), most children bridge this inconsistency in reasoning by age 12; however, I have students in my own classroom (age 14) that give very similar explanations. I think this is largely due to a language barrier. Just as a nine year old fluent in English can have difficulty in connecting their verbal intelligence to their conceptual intelligence, so can an older student whose first language may not be English. Such is the case with my own student population. Many of them may recognize mentally that what is causing the greater amount of displacement of a

3 What Makes Things Float? 3 fluid is the volume of the object, but they are unable to express this; they will often resort to the easiest and quickest vocabulary weight! The second developmental hindrance to understanding density at very young ages is due to the inability to integrate two variables, mass and volume (Kohn, 1993, p.1637). It seems that after much exploration, most students have a firm grasp of the ideas of weight and volume independently. However, when asked to address the question of what makes things float, they often attribute the cause only to weight and fail to integrate volume into the equation. Another less common misconception discussed by both Piaget (1930) and Kohn (1993) involves the amount of water an object in immersed in. Sometimes a student may claim that if we put an object that sinks in water into a larger amount of water, such as a pool, that it would float. In fact, this type of claim was also documented by Duckworth (2001) in her work with adult teachers conducting experiments about floating and sinking. Although I have not encountered this misconception often in my own students, it is worthy to note that the idea that a greater amount of water would affect sinking and floating exposes the underlying missing concept of density being a characteristic property of matter. Many children view weight and density as a temporary property of matter (Kohn, 1993, p. 1639). This misconception is easy to expose and can lead to productive discussions about the topic of density as a unique property of substances. There is more than one misconception that children hold in common with many adults regarding density. The size-weight illusion is one of those. Kohn (1993, p. 1647) found that the greatest number of errors in predicting the floating and sinking outcomes of objects occurred among those objects that had volumes inversely proportional to their mass. In other words, both adults and children had a difficult time with small objects that were heavy and large objects that were light. This is largely due to the fact that real world correlations exist for these two variables. Most objects that are large tend to be heavier than objects that are small. This confusion is less prevalent in older students than younger ones, but does persist into adulthood. I often encounter this illusion throughout the density immersion unit. It

4 What Makes Things Float? 4 often needs to be confronted many times and ultimately rests on how well a student grasps volume and its role in density. There are other misconceptions documented by the authors mentioned in this paper. Misconceptions exist such as, the bearing surface issue discussed by Duckworth (2001), where adult investigators attribute floating and sinking to how much surface area is exposed to water; and the amount of air in an object, where students are convinced that floating objects must have air in them (Duckworth, 2001, p. 6, 9, 11; Hardy, Jonen, Moller, & Stern, 2006, p.307). These ideas tend to arise from other misconceptions and are rooted in the misunderstandings of what surface tension is, and the role air can play in altering the mass and volume of a composite material. Misconceptions in adults regarding density can result from the retention of two parallel explanations of the same concept, a scientific one and a common sense one (Kohn, 1993, p.1640). I often find myself putting on a teacher hat when thinking about scientific concepts in order to approach them critically. However, when discussing those same topics without said hat, I can fall into the traps that are my misconceptions I ve carried with me throughout my life. It seems that many adults as well as scientists retain different representations of the same concept within their memory. Resistance to connecting mass with volume with adult investigators is well documented in Duckworth (2001, p.10). This resistance demonstrates how strong our misconceptions can be and how long we can hold on to them. What it all comes down to is many students have not only one, or two misconceptions, but in the end fail to or are resistant to integrating more than one variable into one concept to explain a complex idea like density (Hardy, Jonen, Moller, & Stern, 2006, p. 308). Most kids want to think that ultimately, floating depends on only one thing (usually they say weight). However, even after being confronted with the obvious inadequacies of this explanation, they come back to it time and time again, often forgetting that they experienced the effect of other factors, such as volume, on sinking and

5 What Makes Things Float? 5 floating. Students need to be given many opportunities to investigate both, volume independent of mass and mass independent of volume to gain a thorough understanding of the effects of each variable on floating. Finally, they need to be given able time to systematically separate those two variables and then integrate them together (Duckworth, 2001, p.40).

6 What Makes Things Float? 6 References Duckworth, E. (2001). Inventing Density. In Duckworth, E., Tell Me More : Listening to Learners Explain (pp.1-41). New York: Teachers College. Hardy, M., Jonen, A., Moller, K., Stern, E. (2006). Effects of Instructional Support Within Constructivist Learning Environments for Elementary school Students Understanding of Floating and Sinking. Journal of Educational Psychology, 98(2), Kohn, A. S. (1993). Preschoolers Reasoning about Density: Will it Float? Child Development, 64(2), Piaget, J. (1930). The Level of Water. In Paul, K., The Childs s Conception of Physical Causality (pp ). New York: Harcourt Brace & Company.