Key words: Energy, Heat, Force, Motion, Work, Mayer, Joule, Colding, Helmholtz, History, Philosophy, Teaching.
2. Authors and Institutions
R. Lopes Coelho, firstname.lastname@example.org, University of Lisbon, M. Marques email@example.com, Secondary School of Alcanena. T. Rocha Homem, University of Lisbon, firstname.lastname@example.org.
Some physicists have pointed out that we do not know what energy is. Many studies have shown that the concept of energy is a problem for teaching. The aim of the present study is to make recourse to the history and philosophy of science in order to understand energy in a simple and clear way. In order to achieve this goal, theoretical and empirical research will be presented.
The theoretical research is presented by a hypertext which consists of 4 parts. In the first, concepts of energy in contemporary textbooks are dealt with. The historical development of the concept is the subject of the second part. On the basis of this, it will be shown in the philosophical part, that the discoverers of energy did not find anything which is indestructible and transformable but rather that the concept of energy underwent a change of meaning and energy was considered a substance towards the end of the nineteenth century. In the fourth part, educational implications are considered. Taking the idea of equivalence, gathered from Mayer’s and Joule’s work, it will be shown, that some problems, which have been pointed by teaching experts, can be overcome. In fact, that idea of equivalence complies with the interpretation presented in textbooks published between the 1860s and the 1920s.
Empirical research looks to verify whether the integration of History of Science topics might help students to understand these concepts better, or not. The students involved in the study belong to four classes in the Education and Training Courses for Locksmiths and Electricians. Two classes belong to the first year of these two courses and the others to the second year. In spite of these classes being equivalent to ninth year at school (aged 14-15), the average age of the students is higher than normal for the education level, educational progress, in general, being low.
The conclusions of the study were based on the completion of Word Association Tests at the beginning and at the end of the module, as well as the completion of a questionnaire, a training record, the planning of an experimental activity and the completion of an activity of recreation of a historical experiment carried out by Robert Mayer.
The results obtained permit the following conclusions:
- There was a great development relative to the number of answers scientifically acceptable in the word association tests, mainly in what refers to the stimuli heat, temperature, energy, work and force;
- At the beginning of the study, students had some alternative ideas, namely:
- Heat and temperature are the same physical magnitude;
- Heat is a substance.
- Comparing the first year students with the second year students who learnt about the concept of energy without reference to History of Science, it can be verified that the students from the first year made more significant progress than those from the second year.
- The students showed interest and engagement in the proposed tasks, more than when the teaching was done with no mention of history of science.
4. Description of Case Study
4.1. In the history of science, we learn that energy was discovered in the 1840s by Mayer, Joule, Colding and Helmholtz. Textbooks on physics usually present Mayer and Joule as the discoverers of energy. Physicists and historians of science agree, therefore, on this point: Mayer and Joule discovered energy. What they discovered is the first question to deal with in order to understand energy. In the present study, a distinction will be made between the experimental, the mathematical and the theoretical part of Mayer’s, Joule’s, Colding’s and Helmholtz’s work. This can be used in order to foster students’ thinking about science.
The discoverers did not speak of energy but rather of force. The term energy was introduced by William Thomson in 1851. An outline of the development of the concept will be given in order to clarify some difficulties with the concept nowadays. A text on the concept of force will provide a historical and philosophical basis, which can be used by teachers in order to make the distinction between force and energy.
The historical approach to force and energy and the reflection on experimental activities performed by scientists and their theories provide a variety of examples in order to address characteristics of scientific knowledge, science as a human enterprise and the nature of science, which can be used by teacher in the classroom.
4.2. The empirical study had the following objectives:
· To lessen the student’s difficulties in the study of the concept of energy;
· To introduce history of science topics in such a way as to facilitate the learning of the concept;
· To compare the effective progress of the students when the introduction of topics of HS is turned to with the effective progress of the students when the traditional method of teaching is turned to;
· To plan experimental activities based on historical documents;
· To recreate experimental activities performed by scientists in the study of energy.
The study developed following these stages:
· Choice of area of research – introduction of topics of history of science into the teaching of Physics and Chemistry;
· Choice of the topic to be studied – study of the concept of energy in Physics and Chemistry in the Third Part of Basic Teaching (aged 13-15);
· Choice of education level of students participating in the study.
· Definition of the objectives of the study;
· Choice of instruments to use in the study;
· Care of study instruments to students involved;
· Analysis of results obtained in the study;
· Comparison of the results obtained with the students referred to;
· Discussion of the results obtained from the educational point of view;
· Final conclusions on the results obtained.
5. Historical and philosophical background including nature of science
Robert Mayer made a journey by boat to Java, as doctor on board. The crew had a good trip but suffered from a pulmonary infection on arrival. On carrying out a phlebotomy, he was surprised at the venous blood being lighter than in the area of Germany. He told us that he suspected he had pierced an artery by mistake but verified that this was not the case. Mayer having observed the difference in the colour of blood, or simply having sworn to observe it, according to him, in this resides the seed of his discovery. The discovery of one of the greatest scientific principles germinated based on the following reasoning. If human venous blood is lighter in hot areas, like the tropics, than in cold areas, like Europe, it will be because, in the former areas, more oxygen is used to maintain body temperature. It would have been suggested that to attain this, something will have to have been spent. The connection of this idea with the science of his time is established through the concept of force-cause.
In his first paper, in 1842, Mayer put forward two questions: what forces are and how they are related to each other. The answer to the first question, tells us only that forces are causes. This statement is not proved. It serves, however, to apply to forces the classical saying 'causa aequat effectum' (cause equals effect). Force is understood as cause in the science of that time (see force). Mayer defends that forces are causes. Nevertheless, Mayer’s concept of cause is not that of mechanics. In this science, which was the foundation of physics, force is the cause of acceleration. For Mayer, force disappears in order to make the effect. Thus, for instance, weight was the cause of falling in mechanics. According to Mayer, the cause of falling is not only weight but also the height of a body, since without height the body does not fall. By falling, the height decreases and the velocity of falling increases. This is the meaning of force-cause defended by Mayer: the ‘force of falling’ diminishes and, in its place, another force ‘motion’ arises.
Joule established the connection with the science of that time through the concept of heat. There were two main theses concerning the nature of heat. According to Rumford (1798, p. 99) or Davy (1799, p. 13-14), heat was motion. According to Carnot (1824, p. 10-11, 28) or William Thomson (1849, p. 315), heat was a substance. Some authors had posed the question, “what is heat?’’, in connection with their experimental works during the first part of the nineteenth century. This was the case of Haldat, (1807, p. 214), Berthollet, in cooperation with Pictet and Biot (1809, p. 447) or Colladon and Sturm (1828, p. 161). Joule’s research concerns this question: heat is either a substance or motion. If heat is a substance, its quantity cannot change. If this is not the case, then heat cannot be a substance. If it cannot be a substance, it can only be motion, according to the science of that time. Joule’s experimental work aimed to show that heat is not a substance. If it is motion, then the question arose of how much motion of mechanical character there must be in order to obtain a unit of heat. This became then the main objective of his experimental work: the determination of the mechanical equivalent of heat.
Colding aimed to prove his idea ‘forces of nature are imperishable’. Observation shows that forces disappear. Colding puts forward the thesis that they are not destroyed but transformed. The elements of this transformation are observable, such as motion and heat. If what is given at first, for instance motion, is capable of being represented quantitatively by q, the effect, for instance heat, must be equal to q. His experimental work corroborates his idea in the following way: the more force that is produced, the more heat appears; the force added does not disappear but becomes heat.
Helmholtz defended the thesis that there are two fundamental forces in nature, living force and force of tension, whose quantity remains constant. The falling of bodies is the paradigmatic phenomenon. The author took the weight in height as the cause of the falling. The cause is designated by force of tension, the effect by living force. In the case of falling, the force of tension and the living force are connected with observable data. In the case of heat, that is no longer true. In the cases where observation is not available, Helmholtz ascribed forces of tension and living forces to observable elements. For instance, the battery, which feeds a circuit, is connected with the force of tension and what is followed with living force. Thus, he generalised mechanical forces to the different domains of physics and did not rule out the possibility of generalising this to life sciences.
The term energy meant activity and had been used with this meaning in the 18th century and in the first part of the 19th. In 1851, William Thomson, later on Lord Kelvin, used the word to refer to the mechanical activity of a body, i.e., its capacity of doing work. The division into two sets – static and dynamical - of the stores of activity availables led to the distinction between potential and kinetic energy. Attempts made in order to adapt the concept to phenomena led to the concept of energy as a substance. This was the reason for criticism and for some of the difficulties with the understanding of energy nowadays. The variety of theses concerning the nature of heat, falling of bodies, energy and the fact that these theses were used to explain phenomena highlight an important characteristic of science: scientific theories include an interpretation of phenomena. Present theses concerning heat, which is a form of energy or transference of energy, force, which is the cause of acceleration or a thing of thought, and energy, which exists or is an abstracted concept, help students to understand that such problems are not only from the past and foster their thinking about science.
6. Target group, curricular relevance and didactical benefit
The target group consists of students of the primary and secondary level. Energy is a fundamental concept in science and important in daily life as well. The historical and philosophical approach enables us to understand some of students’ difficulties and to overcome them.
Empirical research was carried out with students of the 3rd part of basic education (aged 13-15).
The choice of students participating in the third part of basic education for the study is justified on the grounds that the difficulties presented for the students in secondary education, or even higher than this, in relation to the study of energy can be caused by the first contact with the concept. Thus, it is considered that a change in the way of teaching the concept of energy to elementary school students could change the way these students will face study in later years, leading to an improvement in their academic success.
The sample is then made up of students from two classes in the 1st year of the Course of Education and Training for Locksmiths and Electricians and students in the 2nd year of the same courses. It should be noted that studies in Education Research with students of these courses do not exist yet, which gives a particular interest to the present study.
In agreement with the national program of Physics and Chemistry in the courses referred to, the concept of energy is covered in Year 1. Thus, the study was conducted with the 1st year students and using the 2nd year students as a reference, since they had already been taught the concept in the previous school year, using the traditional teaching method.
The study through history motivated the students involved in this study. Students apparently uninterested, with few prospects, at risk of dropping out of school and with low educational attainment have become more committed. Questions and doubts have been raised, by recreating activities already done by great and important scientists. And the result is evident. The associations between the concepts studied increased. There was effective learning and, when comparing the associations made at the end of the study of the module with the associations made with the class that studied the module in a traditional way (without recourse to the history of science) we can conclude that the students learned the concepts better when the history of science was employed.
Further evidence emerged at the time of final assessment, required by our education system. The students claimed they knew nothing; they would not be able to do the test because they did not know the subject. What is certain is that there was only one grade lower than fifty percent in the first year classes and there was no student with a level inferior to three (where 1 is the worst, 5 the best and 3 is positive) in the final evaluation.
7. Activities, methods and media for learning
Original experiments, pictures of them, calculations and interpretations are presented as well as conceptual models of experiments. These enable students to grasp what is important to keep in mind when they have to solve problems.
Images and explanations of Joule’s experiments in contemporary textbooks are discussed.
Concepts of force, such as Descartes’, Newton’s, Mayer’s, Colding’s or Helmholtz’s as well the difficulties pointed out with them and criticism made in the course of history constitute data which can prevent students from misunderstand energy and force.
Teachers could use textbook exercises to discuss the concepts. For instance, a body of 5 kg and 4 meters height falls down. Mechanics teaches us that the potential energy of the body is transformed into kinetic energy. What a student can observe is, however, only the falling. This had already been asserted by d’Alembert, 1743. Lodge said that the energy exists in space and flows in the falling body. Other authors defend that the potential energy exists in both the falling body and the earth. The presentation and discussion of different theses and the confrontation with observation alert students to the difficulty with the connection between theory and experiments.
The empirical research part took place during the physics and chemistry lessons, in the classes in the 1st year of Education and Training for Locksmiths and Electricians, according to the following phases:
3.Reading and interpreting a text on the history of energy;
4.Conducting a formative statement on the text of the history of energy;
5.Planning for re-creating the experiment carried out by Robert Mayer;
6.Re-creation of Mayer’s experiment - experimental activity;
7.Preparation of a report on the experimental work carried out;
8.Exploration of the concepts covered in the experimental activity carried out;
9.Concepts of energy, heat, work and temperature - differences and similarities;
10 International system of units for energy, heat, work and temperature and its relationship with the history of science;
(The description of each stage as well as all material used throughout the study are attached, see results.)
8. Obstacles to teaching and learning
Some physicists have pointed out that we do not know what energy is. If there is no clear idea of what energy is, teaching the concept must be a problem. There has been much research on the subject energy: either on students’ misunderstandings (Watts 1983, Duit 1986, Nicholls and Ogborn 1993, Cotignola et al. 2002, de Berg, 2006, Barbosa and Borges, 2006, and many others) or on teaching methods in order to avoid misconceptions (Solomon 1983, Prideaux 1995, Trumper 1990, 1991, 1997). Explanations of energy in high-school and university textbooks have been criticised: Lehrman 1973, Sexl 1981, Duit 1981, Hicks 1983, Duit 1987, Bauman 1992, Chrisholm 1992, Cotignola et. al. 2002, Doménech et al., 2007.
Duit 1987, for instance, pointed out some inconveniences of the concept of energy as something quasi material, defended by some physicists. According to Beynon 1990, there is so much confusion with energy “because it is not treated as an abstract physical quantity but something real, just like a piece of cheese” (p. 315). Empirical educational research shows alternative ideas such as ‘Energy is fuel’ or ‘Energy is stored within objects’ (Ogborn 1993, p. 73, Prideaux 1995, p. 278). Is there a way to overcome this situation? A positive answer to this question is one aim of the present study.
There is, however, a reason for that concept of energy.The most common presentation of energy in contemporary textbooks states: energy cannot be destroyed nor created but only transformed. If energy can be transformed, then forms of energy must exist. Connected with transformation appears the indestructibility of energy, which reinforces the idea of its reality. Thus, it is understandable that some textbooks present energy as something quasi material, as Duit stressed, and students think of it as something real.
9. Pedagogical skills
It is useful to have knowledge of
· a) the experiments which were important concerning the discovery of the conservation principle (history);
· b) how they were interpreted, which includes the distinction between the experimental work and the theory used, at that time and later on (philosophy);
· c) how the concepts used today, such as ‘energy’, ‘kinetic energy’, ‘potential energy’, ‘forms of energy’ and ‘transference of energy’ appeared (history).
10. Research evidence
· Textbooks are, in general, disappointing when we want to learn something about the history of science.
· Useful literature on the history of energy:
- Bevilacqua, F. (1983) The principle of conservation of energy and the history of classical electromagnetic theory. La Goliardica Pavese, Pavia
- Breger, H. (1982) Die Natur als arbeitende Maschine: zur Entstehung des Energiebegriffs in der Physik 1840–1850. Campus Verlag. Frankfurt a. M., New York
- Caneva, K. (1993) Robert Mayer and the conservation of energy. Princeton University Press, Princeton
- Cardwell, D. (1989) James Joule. A Biography. Manchester University Press, Manchester
- Cassiday D, Holton G, Rutherford J (2002) Understanding Physics. Springer, New York [etc.]
- Coelho RL (2006) O Conceito de Energia: passado e sentido. Opus. Off., vol II. Shaker, Aachen
- Dahl PF (1963) Colding and the conservation of energy. Centaurus 8:174–188
- Elkana, Y. (1974) Discovery of the Conservation of Energy. Hutchinson, London.
- Guedj M (2000) L’émergence du principe de conservation de l’énergie et la construction de la thermodynamique. PhD Dissertation, Paris
- Kuhn, T. S. (1959) "Energy conservation as an example of simultaneous discovery". In M. Clagget (ed.) Critical Problems in the History of Science, p. 321-56. Wisconsin University Press, Madison.
- Smith C (1998) The science of energy: a cultural history of energy physics in Victorian Britain. The Athlone Press, London
- Smith, C. & Wise, N. (1989) Energy and Empire. A biographical Study of Lord Kelvin. Cambridge University Press, Cambridge.
11. Further user professional development
11.1 Useful papers for connecting history of energy and teaching:
· Coelho, R.L. (2009) On the concept of energy: how understanding its history can Improve physics teaching. Sci & Educ 18: 961-983.
· Hecht, E. (2003) An historico-critical account of potential energy: is PE really real?”. The Phys Teacher 41: 486-493.
Valente, M. (1999) Uma leitura pedagógica da construção histórica
do conceito de energia: contributo para uma didáctica crítica. PhD Dissertation. Lisbon.
11.2 Papers about students’ difficulties:
· Doménech et al. (2007) Teaching of energy issues: a debate proposal for a global reorientation. Sci & Educ 16: 43-64.
· Cotignola, M.I. et al (2002) Difficulties in learning thermodynamic concepts: are they linked to the historical development of this field?. Sci & Educ 11: 279-291.
· Prideaux, N. (1995) Different approaches to the teaching of the energy concept. School Sci Rev 77: 49-57.
· Trumper, R. (1990) Being constructive: an alternative approach to the teaching of energy concept – part one. Int J Sci Educ 12: 343-354.
11.3 Papers criticizing textbooks:
Doménech et al. (2007) Teaching of energy issues: a debate proposal for a global reorientation. Sci & Educ 16: 43-64.
Bauman, R.P. (1992) Physics that textbook writers usually get wrong. Phys Teacher 30:264–269
Duit, R. (1987) Should energy be illustrated as something quasi-material? Int J Sci Educ 9:139–145
Hicks, N. (1983) Energy is the Capacity to do Work – or is it?. The Phys Teacher 21:529–530
12. Written resources
- Texts on the development of the concept of energy and force.
- In the empirical research, the following text was read and discussed by the students in the classroom: “Energy... a past that brings us to the present!”: