Aprendizaje de propiedades elementales de la materia: volumen, masa y densidad, en estudiantes de ESO

Resumo

This research expects to contribute to Science Education by designing, implementing and assessing a teaching proposal that will help the ESO (compulsory secondary education) students to assimilate the basic concepts of volume, mass and density, addressed at this stage. With this aim, the research is structured in three studies related to the teaching of such concepts: analysis of alternative conceptions, analysis of textbooks; and production, implementation and evaluation of a teaching proposal. The instruments of analysis used for each study, are indicated in the following lines: Open-answer questionnaires, for the first study (Sample 1). Presence-absence protocols/template, for the analysis of textbooks: Initial and final open-answer questionnaires, structured in five fundamental aspects, related to volume, mass and density; result sheets with the students' answers to the activities from the unit; and, diary and final report of the teacher, for the investigation of the implemented teaching proposal (Sample 2). The results about alternative conceptions indicate that students who finish the third year of ESO, present difficulties in explaining the suggested phenomena. Some of these difficulties are: the association between shape changes and volume changes, the influence of weight or immersion depth on the volume of displaced liquid when a solid is totally immersed in it, the absence of mass in gases or the confusion between density and viscosity; they stand out for being the most unshakable. In addition, it is noteworthy that most of the students in the sample studied are not able to estimate approximate values of mass or volume of common objects in their daily life. Nor do they consider density as a property that serves to differentiate substances from others, and only a few consider that density does not depend on the amount of substance. They use the proper interpretation of flotation better when comparing what happened with the same solid in different liquids, than when the situation contemplates several solids in the same liquid. These circumstances reveal the shortcomings in the teaching strategy used for the treatment of these contents In the analysis of the texts from ESO, we searched for the presence or absence of elements that could be related to the mentioned alternative conceptions, comparing those published according to the previous law (LOE) and those that are governed by the current legislation (LOMCE). In general, books introduce density as a mathematical formula without a prior qualitative introduction to its meaning. Although there are some examples of values of substance densities (with few cases of gases), they do not include examples of materials of possible interest such as graphene. Graphically, only a minority of the analyzed books highlight the contrast between the values of densities of solid substances. The books for the new law are better in this aspect. They do not tackle alternative conceptions related to the fact that the water displaced by a solid in complete immersion does not depend on the weight of the solid or the depth to which it is immersed. But they often reproduce the same example, the "measure of the volume of a stone immersed in water", under the false premise that the students lack previous inadequate ideas about it. In the separation of substances by decantation, the example of water and oil appears systematically. But it is not used to show other examples as the decanting in the purification of the water or the manufacturing of essential oils. The proposal for examples of buoyancy of solids in liquids has improved in some books by certain publishers when moving from one law to the next one. But aspects such as the variable buoyancy of an object in the same liquid are not discussed in any of the books analyzed. Finally, the teaching proposal is based on the directed research methodology and applied to students from the third year of ESO. It consists of a program of activities (23, of experimental type, in seven sessions), that follows a sequence based on the idea of palliating the difficulties that have been anticipated in previous studies. The methodology, in general, consists in starting with a problematic situation of interest from which the students give initial hypotheses. Then, they must think of some method that leads them to check these hypotheses, obtaining data and conclusions. The role of the teacher is to guide the learning process. The participants were the students (of two homogeneous groups) of the researcher. After the development and the analysis of the proposal, the results reveal, first, a significant improvement between pre-test and pos-test responses. This includes the assimilation that the volume of liquid displaced by a solid completely submerged in it depends on its volume, the use of density for the identification of substances, the differentiation between density and viscosity or the assimilation that the gaseous state has the same properties as the other states. Likewise, we observe a progressive adaptation to the proposed teaching methodology and a greater autonomy in the development of experimental work. This development occurs mainly in those procedures related to the identification of the proposed problem, the formulation of predictions and hypotheses and the establishment of conclusions. However, we detect some intermittence in the measurement of magnitudes, collection of data and use of basic laboratory techniques, according to the sessions and activities, aspects in which we consider necessary to continue working. Finally, we also notice an improvement in the attitude towards the learning of science. However, there has been a need to expand the number of examples in which to apply knowledge, to ensure that some of the more deeply rooted alternative conceptions are overcome and that this is extended to a majority of students.