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Asia-Pacific Forum on Science Learning and Teaching, Volume 18, Issue 2, Article 18 (Dec., 2017) |
Law of Mechanical Energy Conservation
The law of mechanical energy conservation has gained so much attention (Solbes, Guisasola, & Tarín, 2009) due to which it remained as a subject of interest for many physicists. Although the conservation of mechanical energy forms a fundamental part of any introductory physics (Hwu, 1980; Hassani, 2005; Santos, Soares, & Tort, 2010; Li, 2012; Bambill, Benito, & Garda, 2004) and classical mechanics (May, 1936), the students are able to solve only the simple energy problems and not the ones that involves principles of energy conservation (Speltini & Ure, 2002). Further, the concept of energy conservation is widely misunderstood and accepted in a manner that is not parallel with the scientific point of view (Solbes et al., 2009). This is often because the students are unaware in the usage of the word while describing the law of mechanical energy conservation. Students are often confused with the term “conservation” because they assume it as a synonym to “saving” (Tatar & Oktay, 2007; Mweene & Mumb, 2012) or not wasting energy. The students are able to remember and recite the law of mechanical energy conservation with a relative easiness, but are unable to apply correctly in real situations (Tatar & Oktay, 2007; Mweene & Mumb, 2012). As asserted by Driver and Warrington (1985), students consider energy not as a conserved quantity, but something that is active for a short while and disappears.
By conservation, Millar (2005), Featonby and Jeskova (2012) and Needham (2011) defines that the total amount of energy, both in the beginning and the end remains the same, no matter what kind of processes or events takes place. This means that energy can neither be created nor destroyed (Tatar & Oktay, 2007; Wisniak, 2008; Daane et al., 2013; Larmer, 2014; Herrmann-Abell & DeBoer, 2011; Mweene & Mumb, 2012). In principle, energy is a conserved quantity (Driver & Warrington, 1985) and that same quantity remains constant at the end as was in the beginning of the process (Daane et al., 2013). Feynman (1963) further highlights the fact that this numerical quantity does not change even when there are manifold changes of nature and its processes. Even after the tricks of the nature and repeated transformations; the quantity remains the same throughout as we calculate all forms of energy in the system again (Feynman, 1963). Precisely, the law of mechanical energy conservation means that the energy can change from one kind to another, but at the end, the total energy involved in the system always remain the same. The energy which was present in the beginning might have turned out to be in a different form during the process, but the total amount of that energy at the end of the event always remains the same as it was in the beginning.
In Newtonian mechanics, the law of mechanical energy conservation implies that the sum of the potential energy and the kinetic energy is always constant in an isolated system (Wisniak, 2008; Santos et al., 2010). This means that for the particular system, the total amount of energy can only be changed if the energy is transferred into that system or if the energy is being transferred out of that system. In an isolated system, there is no transfer or exchange of energy across the boundary of the system while transfer of energy is possible across the boundary of the non-isolated system either by one or more mechanisms (Jewett, 2008). The law of mechanical energy conservation takes place only in an isolated system. The energy and mass are always maintained constant in an isolated system because neither of these two physical quantities gets transferred across the boundary. In such system, it allows the transfer of energy within itself but restricts completely with the surroundings. However, the existence of such isolated systems is only theoretical and that they in reality do not exist at all. But for the sake of scientific experiments, most of the non-conserved forces such as friction and gravitational forces are often neglected and claimed negligible even if we know that their existence is inevitable and pervasive.
Previous studies on Law of Mechanical Energy Conservation
Neglecting the presence of the non-conserved forces, various attempts have been made to study the law of mechanical energy conservation. It was studied based on the Galilean principle of relativity focusing both on conservation of linear momentum and angular momentum (Santos et al., 2010) and by using a projectile motion (Hwu, 1980). The bowing effect on energy conservation using an inclined experiment (Li, 2012) was also studied by assuming that there exists no friction on a dynamic track used for the experiment. Similarly, in the study of the conservation of mechanical energy in the theory of inviscid fluid sheet by Shields and Webster (1989), it was found that mechanical energy is conserved. Bambill et al. (2004) has also explained the law using a conical pendulum while a video analysis was used to study the motion in the laboratory (Bryan, 2010).
Speltini and Ure (2002) have conducted a study based on an exploratory approach with 114 students to find conservation principles, meaning of conservation and examples of both conservation and non-conservation. Daane et al.(2013) involved K-12 teachers to study the concepts, including conservation, amount and forms of energy and its usefulness while Brook and Wells (1988) have surveyed the understanding of energy and energy conservation of 10 teachers and students aged 11-15 and observed that the majority of them had limited understanding of conservation. 28 students who have already studied relevant ideas in physics was also investigated to trace the extent to which students used energy conservation ideas in solving both written and practical problems (Driver & Warrington, 1985). It was illustrated that the concept of energy conservation was rarely used in analyzing a problem. In a study by Solbes et al. (2009) a teaching sequence has been designed and assessed to introduce the concepts of energy conservation at post-secondary students and revealed that the teaching sequence if combined with a methodology used in the classroom may effect a better understanding of law of mechanical energy conservation. Mweene and Mumb (2012) involved 90 university biology students to assess understanding of energy conservation using a pencil and paper test and observed that students have no concept that the energy is not lost. Also, there is a study that involved 9739 middle and 5870 high school students and 176 university students to assess about energy concepts, energy transfer and transformation and energy conservation using a standard-based multiple choice (Herrmann-Abell & DeBoer, 2011). The study revealed that the students had difficulties with items related to conservation and its application to a specific real-world.
In achieving scientific literacy, the inquiry-based approach of teaching have been widely regarded as an effective method (Duran, McArthur, & Van Hook, 2004) because it involves recognizing assumptions, using critical and logical thinking and also considering alternative explanations (National Research Council, 2000). Several other studies have also revealed an empirical evidence in claiming inquiry method as a medium that develops personal meaning which may boost higher science achievement (Secker & Lissitz, 1999; Duran et al., 2004; UNESCO, 2009). This method is also noted for the benefit that it builds a close relationship between the processes and conceptual ideas of science (Tytler, 2007). Moreover, inquiry based education is often supported for being effective in addressing higher basic education attainment, increased motivation of both teacher and student for science and for the positive contribution through the success in science (UNESCO, 2009). Hence, in science education the teachers are encouraged to engage inquiry on a daily basis in their teaching (Jackson & Wenning, 2010).
In inquiry-based science education, the students are engaged to develop knowledge, understand ideas and thinking processes used by the scientists in producing new knowledge (Abdi, 2014) and understanding the natural world (National Research Council, 1996). It is a pedagogical setting that depends less on textbooks as a main resource for information, but more on hands-on approach making students as the central to the learning episodes (Duran et al., 2004). So, like the scientists do, the students investigate the things or events and propose based on the findings of their investigations. In this teaching approach, the teacher provides the materials and problems for the students to solve while the teacher assists as a facilitator. In a guided inquiry classroom the students and the teachers work together collaboratively to meet the desired goals (National Research Council, 1996). The students take a lead role in investigating the problem by formulating hypothesis and frame some solutions. The data collection, interpretation and findings are also done by the learners. The students are able to generalize their finding at the end of an activity (National Research Council, 1996; Nivalainen et al., 2013).
As much as guided inquiry offers active and meaningful learning, laboratory has been yet another approach with similar benefits. It is a setting in which students learn lessons persistently by using a variety of materials with motivation (Koc, Okumus, & Özturk, 2013). It was widely used in science where there are more demonstration activities (Blosser, 1980) because the students learn through examination and manipulation of the materials to develop the concepts and knowledge of that scientific phenomenon, thus enhancing their understanding of the scientific concepts (Tsai, 2003; Hofstein & Mamlok-Naaman, 2007). The students learn to make hypotheses and follow scientific investigations, formulate and revise scientific explanations and engage in defending scientific arguments (Hofstein & Lunetta, 2004) besides obtaining skills of manipulation, observation, critical thinking, scientific interpretations and cooperation. In physics, Alimen (2009) describes such laboratory activities as a kind of a social learning process where they cooperate each other to achieve their goal. The students become active doers (Flick, 1993; Haury & Rillero, 1994) which can consequently enhance their own learning and retrieval for a longer period of time (Ruby, 2001).
In this developed guided inquiry laboratory, all those typical characteristics of both guided inquiry approach and laboratory learning are blended to provide students a better way of understanding the law of mechanical energy conservation. In this setting, the intervention of the inquiry process is planned, targeted and supervised based on the constructive approach of learning (Kuhlthau & Maniotes, 2010).
The hands-on activity is one of the most meaningful learning strategies because it encourages the learners to directly perform the specific task in order to learn about it. It allows the students to “learn by doing” (Trivedi & Sharma, 2013) as they have freedom in making judgments after observation, interpretations and manipulations (Ruby, 2001). This mode of learning “Science by Doing” actively engage and encourage the students to investigate science which ultimately works on the principle that “doing” results in understanding and excitement (Tytler, 2007). In such learning environments, the students handle specific scientific instruments and manipulate the objects that they are studying (Rutherford, 1993). This helps them to create a relationship between the pieces of knowledge and enable the information to be compared both by its abstract meaning and physical illustration (Ruby, 2001). Another notable educational component of hands-on methodology is that the experiences of the students are placed first while other methods depend heavily on teacher experience (Stohr-Hunt, 1996). Hands-on science has been proposed as one means to increase students’ achievement in science education (Ruby, 2001). Kolb (1984) in his Experiential Learning Theory (ELT) beliefs that in order to promote meaningful learning in children, they have to physically interact with the materials. Accordingly, the children can engage and have a direct experience which can improve reflective skills and retentions (Haury & Rillero, 1994). The hands-on learning encourages a learning through action, experience, discovery and exploration, thereby making the learners understand the real-life illustrations of the knowledge (Haury & Rillero, 1994).
Assessing the understanding of students is one of the most complex tasks for many educators or academic institutions, but it is necessary in order to figure out what learners know and have understood. It is useful in investigating the impact of any intervention or treatment used in teaching the concepts. It is only when the instructors understand such differences that it can meet the diverse learning needs of all the students (Felder & Brent, 2005). When the students do not understand the concepts that they are taught, they maintain their own way of learning and risks to the formation of misconceptions that are later challenging to correct. Hence, the process of assessing student learning as a part of our teaching is very important because it provides teachers a valid information on what our students are learning (Drake & Barlow, 2007).
Thus, in an attempt to investigate and classify the students’ level of understanding, this study used a categorization method which was modified from Abraham, Williamson, and Westbrook (1994). Of the five levels of understanding (Abraham et al., 1994) namely Sound Understanding (SU), Partial Understanding (PU), Partial Understanding with Specific Alternate Conception (PUSAC), Specific Alternate Conception (SAC) and No Understanding (NU), the Partial Understanding (PU) was excluded since the two-tiers items used in this study was not suitable to evaluate a response that included at least one of the components of a validated response (Abraham et al., 1994). The more details on its classification is explained in the data analysis.
