A descriptive study of pre-service science teachers’ misconceptions about sinking

The meanings attributed to the concepts have been changed and developed because of the rapidly changing developments in scientific knowledge. Not only does this situation lead conceptual learning to be one of the most important subjects in science education, but also increases the importance of research in this area (Joung, 2009). The studies have shown that there are a lot of factors that affect the students’ concept learning (Kiray, Gok, & Bozkir, 2015).

Experience is the one of the most important factors. Before coming to the classroom, the students have prior experiences of the world resulting from their previous interactions, which affect their learning during their education at school (Yin, Tomita, & Shavelson, 2008). Along with the students’ incorrect prior knowledge gained from real-life experiences and observations, teachers’ incorrect descriptions in the school, the reflection of the authors’ misinformation in textbooks, and the daily misuse of the scientific concepts may cause students to ascribe different meanings to the scientific concepts (Unal & Costu, 2005; Sahin & Cepni, 2011). Students’ mistaken “scientific” knowledge is called misconceptions, misunderstandings, alternative frames, or alternative conceptions (Arslan, Cigdemoglu, & Moseley, 2012). Although there are many studies that deal with a specific science concept (Kirbulut & Beeth, 2013), this study focused on the pre-service science teachers’ misconceptions of scientific concepts related to floating and sinking.

The floating and sinking misconceptions
Even though the students have encountered the topic of floating and sinking, they still have many misconceptions about it. The content is quite complex as it is associated with many content areas. In order for students to understand the floating–sinking topic, they should comprehend pressure, pressure force, density, buoyancy, buoyant force, balanced and unbalanced force, gravity, weight, and the principle of Archimedes (Bulunuz, Bulunuz, Karagoz, & Tavsanli, 2016, Cepni, Ayas, Johnson, & Turgut, 1997; Heywood & Parker, 2001; Hewit, 2002; Leuchter, Saalbach, & Hardy, 2014; Moore & Harrison, 2014; She, 2002; Yin, Tomita, & Shavelson, 2008; Yin, Tomita, & Shavelson, 2014). One of the most fundamental misconceptions related to floating and sinking arises from deciding if the matter can float or sink.

To determine whether an object floats or sinks, the density of the liquid and the density of the object should be compared (Kawasaki, Herrenkohl, & Yeary, 2004). This approach is called, “relative density approach” (RDA) in this study. Even though RDA is the most widely used approach to teach the floating and sinking content, the students still have misconceptions about it because of the misconceptions about the objects’ density (Arce, Bodner, & Hutchinson, 2014). The studies have shown that the students assume that the change in density of a liquid induces change in buoyancy of an object; the density of a floating object is more than the density of a sinking object, and the density of an object hanging in a liquid is equal to a floating object’s density (Unal, 2008). Also, they consider that when an object’s density increases, the buoyancy of the object always decreases, (She, 2002) and objects that are covered by the liquid have always the same density (Unal & Costu, 2005). In addition to the above misconceptions regarding RDA, the students have the misconceptions about the forces that act on the floating and sinking objects.

The students consider the forces that impact the objects to understand the topic of floating and sinking (Heywood & Parker, 2001). In other words, the students use reasoning about the balanced and unbalanced forces (Moore & Harrison, 2004). Relative Force Approach (RFA) is defined as the comparison of the magnitude of an object’s weight with the magnitude of the object’s buoyant force in this study. The students usually are not aware of the RFA (Relative Force Approach) that compares the magnitude of the objects’ weights with the magnitude of the buoyant force. The students should master the principles of Archimedes to comprehend RFA.

According to the principles of Archimedes, the magnitude of the upward buoyant force, which is applied on a sinking object or floating object, is equal to the magnitude of the liquid’s weight that the body displaces. This principle applies to both the floating and sinking objects. However, there is a special case for the floating objects. When an object floats in a liquid, the magnitude of the buoyant force is equal to the magnitude of the overflowing liquid’s weight and object’s weight (Besson, 2004; Hewit, 2002). For a sinking object, only the magnitude of the buoyant force is equal to the magnitude of the weight of the overflowing liquid, and the magnitude of the object’s weight is greater than the buoyant force. This situation may lead to students having a misconception about the content (MEB, 2006).

Some of the misconceptions are that the heavy objects displace more liquid than the light objects, and the sinking objects displace less liquid than the objects hanging in liquid (Cepni & Sahin, 2012; She, 2002). In addition, the hollow objects relocate more liquid (i.e., boat-shaped objects) than the solid objects, and the floating objects relocate more the liquid volume because of their big surface areas (Hewit, 2002; She, 2002).

The students have several misconceptions about overflowing liquid, the effects of the volume, or amount of the liquid when determining if an object floats or sinks. First, they believe that the volume of the liquid determines whether an object sinks or floats (Cepni & Sahin, 2012; Unal & Costu, 2005; Unal, 2008). Second, they assume that when the volume of a liquid in a container is increased, the volume of submerged part of a floating object increases (Unal, 2008). Third, they deem that an object would float if the object’s volume and weight increases (Cepni & Sahin, 2012; Yin, Tomita, & Shavelson, 2008). These misconceptions affect the students' understanding the floating and sinking content.

Furthermore, the students develop misconceptions about the buoyant force. Many students think that if the volume of an object increases, the buoyant force increases. The students also believe that the buoyant force would be greater when a floating object (out of water) crosses a deep place than when the object crosses a shallow place (Cepni & Sahin, 2012; Unal & Costu, 2005; Unal, 2008). Similarly, the students think that when the volume of the liquid decreases, the buoyant force decreases, too, if the greater the floating part (out of water) of an object, the greater its buoyancy (Cepni & Sahin, 2012; Unal, 2008). Moreover, the students believe that the buoyant force of the sinking objects is greater than the buoyant force of the floating objects (Cepni & Sahin, 2012; Unal & Costu, 2005) and the buoyant force only affects the floating objects and does not affect the sinking objects (Cepni & Sahin, 2012).

The students also have a hard time comprehending the pressure force (Psillos, 1999), which causes misconceptions about floating and sinking. The buoyancy is the net force between the pressure force applied to the object from the bottom and the pressure force exerted the object on the top (Besson, 2004; Hewit, 2002). An object floats if the magnitude of the buoyant force is equal to the weight of the object. The misconception about this topic affects the students’ understanding of the pressure force, the buoyant force, and floating and sinking. Even, some students may develop the misconception that the amount of the liquid affects the pressure force of the object (Besson, 2004). Similarly, many students have misconceptions related to the impact of the pressure force on an object because they do not count the force that affects an object in a liquid from either bottom or top. The students do not recognize that the pressure forces cause the buoyant force (Besson, 2004).

The other misconception held by the students is about how an object’s shape affects whether the object floats or sinks. The most common misconceptions about floating and sinking are related to an object's size, weight, or shapes. The students decide whether an object floats or sinks by considering the object’s weight or mass (Cepni & Sahin, 2012; Leuchter, Saalbach, & Hardy, 2014; Moore & Harrison, 2004; Unal & Costu, 2005). For instance, many students expect that a big piece of wood would sink, yet a small piece of iron would float (Leuchter, Saalbach, & Hardy, 2014). The students’ prior experiences cause them to think that the weight or volume of an object determines whether the object floats or sinks. The students use faulty reasoning to determine whether an object floats or sinks by considering the shape of a ship, as a giant ship floats on the sea (Havu-Nuutinen, 2005; She, 2002; Tao, Oliver, & Venville, 2012). Additionally, the students believe that if an object sinks, the object’s weight is greater than water (Ozsevgenc & Cepni, 2006) and that if the weight of the liquid is equal to the object’s weight, the object sinks (Havu-Nuutinen, 2005). They also assume that while a small and light object floats, a heavy object sinks (Cepni et al., 2010; Cepni & Sahin, 2012; Kang et al., 2005; Moore & Harrison, 2004; Yin, Tomita, & Shavelson, 2008).

The students also have misconceptions related to the objects’ shapes and features. Several studies have shown that the students believe that the objects float because of their shapes (Havu-Nuuiten, 2005; She, 2002); the objects with holes or empty objects always float (Havu-Nuuiten, 2005; Moore & Harrison, 2004; She, 2002), and the solid or hollow objects sink (Havu-Nuuiten, 2005; Yin, Tomita, & Shavelson, 2008). Moreover, they consider that when a floating object is cut into two parts, the parts would sink (Unal & Costu, 2005). The flat objects float (Yin, Tomita, & Shavelson, 2008), and an object with a hole sinks (Havu-Nuuiten, 2005; Unal & Costu, 2005), such as while a can floats, a closed cab sinks (She, 2002).

Furthermore, the studies have shown that the students believe that the way an object is dropped into the liquid affects whether an object sinks or floats. The students believe that vertical objects sink, and the horizontal objects float (Yin, Tomita, & Shavelson, 2008). In addition placing an object on its sharp edge causes it to sink while placing the object on its wide edge causes it to float (Kıray, 2010; Yin, Tomita, & Shavelson, 2008). Additionally, the students believe that the soft objects float while the rigid objects sink (Moore & Harrison, 2004; Yin, Tomita, & Shavelson, 2008).

Importance of the Study
The students and teachers’ conceptual understanding, teaching, and learning of these concepts have been one of the most important parts of research in science education for the last thirty years (Duit & Treagust, 2003). The majority of the researches about conceptual learning have focused on the students’ comprehension of scientific concepts, even though many teachers and students develop misconceptions. The teachers reinforce these misconceptions by reflecting them in their lesson plans and teaching (Arslan, Cigdemoglu, & Moseley, 2012); therefore, it is important to determine the pre-service science teachers’ misconceptions and correct them. In the literature, the misconceptions about floating and sinking were determined by asking multiple-choice questions and open-ended questions. In this study, the authors investigated the pre-service science teachers’ misconceptions about floating and sinking using a three-tier test. The study sought to answer the following two questions:

What were the pre-service science teachers’ misconceptions related to floating and sinking?
What were the levels of pre-service science teachers’ scientific knowledge, lack of knowledge, lack of confidence, and misconceptions about floating and sinking?