Academic journal article Science Scope

Diagnosing and Dealing with Student Misconceptions: Floating and Sinking

Academic journal article Science Scope

Diagnosing and Dealing with Student Misconceptions: Floating and Sinking

Article excerpt

When students enter the classroom, they often hold prior knowledge or conceptions about the natural world. These conceptions will influence how they come to understand what they are taught in school. Some of their existing knowledge provides good foundations for formal schooling, such as sense of number and language. Other prior conceptions, however, are incompatible with currently accepted scientific knowledge; these conceptions are commonly referred to as misconceptions (NRC 2001). Usually students derive misconceptions through limited observation and experience. Consequently, learning is not only the acquisition of new knowledge; it is also the interaction between new knowledge and prior knowledge. For example, everyday life experience leads young children to believe the Earth is flat. Learning that the "Earth is round," some children then believe that the Earth is like a pancake--round but still flat (Vosniadou and Brewer 1992). To fully establish scientifically justifiable conceptions of the natural world, sometimes students have to experience conceptual change (Carey 1984) and transform misconceptions to complete and accurate conceptions (NRC 2001).

To facilitate students' conceptual change toward a scientific understanding of the natural world, teachers have to (a) identify students' current conceptions about the topic; (b) guide students to realize the limitations of those misconceptions; and (c) guide students to recognize the universality of the scientific conception. Misconceptions broadly exist in a variety of subject areas, such as physics, biology, geography, and other sciences. Among them, bringing students to an understanding of why things sink and float has proved to be one of the most challenging topics for student conceptual change.

Conceptions about why things sink and float

Why things sink and float (WTSF) is addressed in many middle school physical science curricula. Although sinking and floating is a common phenomenon in everyday life, it is a sophisticated science topic. To fully understand the fundamental reasons for WTSF requires complicated knowledge that includes an analysis of forces (buoyancy and gravity) and water pressure. That knowledge, however, is either not introduced or not sufficiently addressed in middle school curricula. Rather, some curriculum developers take a shortcut and use relative density as a simplified explanation for WTSF (e.g., Pottenger and Young 1992). Even so, relative density itself is challenging for many students because density is a concept involving the ratio of mass to volume (e.g., Smith, Snir, and Grosslight 1992) and relative density involves comparing two ratio variables.

Despite its complexity in science, sinking and floating is such a common phenomenon that almost all students have rich experiences and personal "theories" or "mental models" for explaining WTSF. Unfortunately, many of their "theories" are either misconceptions or conceptions that are only valid under certain circumstances. Based on research literature and an experiment involving 1,002 sixth and seventh graders, we have summarized 10 misconceptions that middle school students commonly have about sinking and floating (see Figure 1) (Yin 2005).


Diagnostic items for common misconceptions of WTSF

a. Misconception I: Big/heavy things sink,
small/light things float.

Block A and Block B both float in water. Suppose that we
glue them firmly together and place them in water; together
they will --.


Correct answer: float
Misconception answer: sink (or subsurface float)

B. Misconception II: Hollow things float;
things with air in them float.

Ball A and Ball B are made of different materials, but
they have the SAME mass and the SAME volume. Ball
A is solid; Ball B is hollow in the center (see the pictures
below). Ball A sinks in water. When placed in water, Ball
B will --.


Correct answer: sink
Misconception answer: float (or subsurface float)

C. … 
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