CTS Guide: Transfer of Energy, pp. 192-193- Section IV Research Summaries
Thermal Energy, Heat, and Temperature
Millar (2005) points out how students misuse heat as a synonym for thermal energy. In students’ everyday language, heat is something hot objects possess and if heat is added, temperature rises. If heat is lost, temperature falls. Many students do not regard cold objects as having “heat energy.”
Studies by Kesidou and Duit (1993) and others revealed the commonly held idea that “heat energy” depends on the temperature of an object and that objects with higher temperature have more “heat energy” regardless of quantity.
Thermal energy is an unexpectedly difficult concept for students to grasp, as temperature is often mistaken as thermal energy. Most children can’t distinguish between heat and temperature in grades K–4. They may think that some materials are intrinsically warm (blankets or mittens) or cold (metals). Cold is often thought of as an entity like heat, with many children thinking that cold is the opposite of heat rather than being part of the same continuum (Driver et al. 1994).
One place students would be expected to understand the distinction between heat and temperature is in chemistry classes. However, most of the chemistry problems assigned to students in introductory chemistry classes do not require students to make the distinction, so students have little opportunity to acquire the distinction. Chemistry teachers may be unaware that students lack this skill and may have the expectation that they do understand the difference (Gabel and Bunce 1994).
In a case study of a fifth-grade classroom, students were sure that winter clothes “warmed us up.” When asked what would happen to a thermometer if they put it in their hats, coats, or mittens, students predicted the temperature would go way up. They tested their idea and were not convinced when they saw the temperature had not changed. They thought the thermometer needed to be inside the warm clothes for a longer period of time. Even when they left it in longer, they still were not convinced. They reasoned that somehow cold air was getting inside. This case revealed how strongly held alternative ideas can be and how resistant students can be to change, even with evidence (Watson and Konicek 1990).
Studies in England found that even though many 14- and 16-year-old students have been exposed to formal instruction about heat, most students still seem to associate the term heat with the meanings they have constructed for it during their everyday encounters with hot and cold objects rather than from those encountered in the classroom. Students gave various responses to researchers to describe the difference between heat and temperature, including (1) there is no difference between them (the most common response), (2) temperature is a measurement of heat, and (3) temperature is the effect of heat (Erickson 1985).
Studies have discovered a vast store of ideas about thermal phenomena in children ages 10–12—for example: heat makes things rise, heat and cold are material substances that can be transferred from one thing to another, and heat accumulates in some areas and flows to others (Erickson 1979, 1980).
Researchers have found that children have difficulty understanding heat-related ideas (Harris 1981). It has been suggested that much of the confusion about heat comes from the words we use and that children tend to think of heat as a substance that flows from one place to another.
Erickson’s (1979) early study of heat and temperature reported that children tend to think of temperature as the amount of heat that an object has with no distinction between intensity and amount. Some children thought temperature was related to size or properties of matter.
Energy Transfer, Conductors, Insulators
Middle school students often do not explain the process of heating and cooling in terms of “heat energy” being transferred. When transfer ideas are involved, some students think that cold is being transferred from a colder to warmer object. Other students think that both heat and cold are transferred at the same time. Students do not always explain heat-exchange phenomena as interactions. For example, students may say that objects tend to cool down or release heat spontaneously without acknowledging that the object has come in contact with a cooler object or area (AAAS 2009).
In studies of fourth-, fifth-, and sixth-grade students, a commonly held idea was that heat transfers from a hot object and cold transfers from a cold object. Students who believe this conceptualize heat as a transferring material that is separated into categories of hot and cold (Choi et al. 2001).
In a study of adolescents, adults, and scientists, Lewis and Linn (1994) found a classic separation of “school knowledge” and “everyday knowledge” about thermal phenomena in each of the populations they studied. All three groups had firmly established intuitive ideas including the idea that metals can “trap” or “hold” cold better than other materials and aluminum foil is a good insulator for keeping cold objects cold. These ideas are widespread and multi-generation. When students were asked students whether wool would be an effective wrapper to keep an object cold, the common response was “no”: “No, wool warms things up.” “No, because air can go through the wool, so the drink inside would warm up.” “No, wool conducts heat.” Further questioning revealed that they believed air would flow freely through wool, prohibiting it from insulating objects. In further discussions of how wool keeps them warm, it became clear that they perceived wool as somehow generating heat, rather than simply trapping the heat from their own bodies. As a result, students state that wool is better for keeping things hot, rather than cold. The adults interviewed had similar ideas and recalled wrapping cold things in aluminum foil from their own experience.
Middle school students have been found to successfully manipulate variables in classroom experiments that involve thermal events; yet, they vary greatly in their ability to apply their results to everyday phenomena (Linn and Songer 1991). For example, when students perform insulation and conduction experiments, they measure the changes in temperature over time for hot water in both a disposable foam cup and a glass cup. They make good predictions and give good explanations of their results in terms of a foam cup being a better insulator than glass. However, when the same students are asked to choose a material to help keep a soda cold, 75% choose aluminum foil over foam (Lewis and Linn 1992).
Lewis’s study (1987) found that 75% of interviewed adolescents and adults were adamant that aluminum foil was an excellent insulator. Those interviewed gave personal testimonial evidence of the effectiveness of wrapping cold drinks, cold apples, and cold yogurt in aluminum foil, including lengthy descriptions of how their friends and parents used aluminum foil to wrap cold foods. One adult even shared how she had proof by describing how she frequently wrapped cold foods in aluminum foil for her children’s lunches and her mother had done the same thing for her.
Studies show that children have difficulty thinking of heat conduction when they feel a cold surface. They seem to think that the sensation of coldness is due to something leaving a cold object and entering the body. In a study of 300 15-year-old students, most thought of coldness as being the entity that was transferred (Brooks et al. 1984).
Mixing Two Liquids of Different Temperatures Together
When considering the final temperature of two beakers of cold water at the same temperature mixed together, children ages 4–6 often judge the temperature to be the same. However, children ages 5–8 often say that the water will be twice as cold because there is twice as much water. At age 12, students describe the water as being the same temperature when mixed together, much like the very young children. One possible explanation for this progression is that young children do not consider amount and judge temperature as if it were an extensive physical quantity. Older children are better able to differentiate between intensive and extensive quantities, understanding that temperature remains unchanged despite the amount of water. It was also found that children tended to make more correct predictions of temperature when equal amounts of hot and cold water were mixed than when two equal amounts of cold water were mixed (Driver et al. 1994).
Researchers have found that difficulties experienced by students in response to questions that ask them to predict the final temperature of a mixture of two quantities of water, given the initial temperature of the components, depend on the form in which the temperature problems are presented. Qualitative tasks in which the water is described as warm, cool, hot, or cold are easier than quantitative ones in which specific temperatures are given. Erickson and Tiberghien (1985) found that younger students (ages 8–9) prefer an addition strategy, whereas older students are more apt to use a subtraction strategy, which at least acknowledges that the final temperature lies somewhere in between. However, students ages 12–16 were as likely to use an addition or subtraction strategy as they were to use an averaging strategy.
Thermal Equilibrium
Examining several studies on elementary students’ understanding of heat equilibrium, researchers concluded that the findings indicate that students were unable to comprehend that the temperature of a material changes according to the temperature of the surrounding air. Thus, it appears that students do not readily form accurate concepts about heat equilibrium (Paik, Cho, and Go 2007).
A study by Choi et al. (2001) of 9- to 11-year-old students revealed that they did not recognize that different materials could have the same temperature under equal conditions. Students assumed that materials were categorized by cold, medium, or hot. They described metals as being “cold by nature” and a cloth as being “warm by nature.”
Students ages 8–12 are able to use and read a thermometer to take temperature readings. They tend to make judgments about the temperature of an object based more on the nature of the material than the temperature of the surrounding medium. Students are likely to think that objects of different materials in the same room will be at different temperatures even if they are told that the objects are kept at room temperature (Erickson 1985).
The concept of thermal equilibrium when several objects are in prolonged contact with the same air in the same room is often missing. Students have difficulty recognizing the equality of temperatures at thermal equilibrium (Tiberghien 1985).
Engel Clough and Driver (1985) questioned 12-year-old students about temperature. Some students said metals were colder substances than plastic. Many children referred to metals “pulling in heat” or heat being released easily by metals.