1 Manuscript accepted for publication in Science & Education Understanding the Role of Measurements in Creating Physical Quantities: A Case Study of Learning to Quantify Temperature in Physics Teacher Education TERHI MÄNTYLÄ and ISMO T KOPONEN Department of Physical Sciences, University of Helsinki, FINLAND (E-mail: terhi.mantyla@helsinki.fi) Abstract. Learning to understand the content and meaning of physics’ concepts is one of the main goals of physics education. In achieving this understanding, the creation of quantities through quantitative measurements, or rather through quantifying experiments, is a key process. The present article introduces a didactical reconstruction for understanding the construction of the meaning of physical quantities from a network point of view, where the quantities are part of networks and the quantifying experiments build up these networks. As a practical example, we discuss how the quantity temperature is constructed in an instructional unit designed for student teachers and what the learning outcomes are. 1. Introduction In physics education, conceptual understanding refers to the understanding of the content and meaning of concepts, with an emphasis on qualitative understanding. Part of conceptual understanding is to learn to understand ‘how we know what we know’. In physics, knowledge of ‘how we know’ goes back to question of how concepts acquire their meaning and empirical support. This is inherently related to measurements, which transform the concepts into measurable physical quantities. The formation of quantities through quantitative experiments or measurements is not often seen as a part of conceptual understanding, or at least it is treated as a nonproblematic part of it. The purpose of this paper is to discuss the advantages that can be gained by focusing on the role of quantitative (or quantifying) measurements. This is done in the context of physics teacher education, because the teachers in particular need to be able to answer the question of ‘how we know what we know’, and moreover, be able to reflect this understanding in their teaching. In reaching the goal of better conceptual understanding, the history and philosophy of science (HPS) can serve us in many valuable ways; the conceptual analysis of physics history helps us to regenerate the knowledge of physics by answering the questions: how did we come to believe what we believe, and how did we discover what we know (compare with Chang 2004, pp.236-240). However, our purpose is not to produce historical reconstructions, but instead to use HPS as a starting point for developing and designing suitable didactical solutions, which can be called didactical reconstructions for teaching (Izquierdo-Aymerich & Adúriz-Bravo 2003). For this purpose we introduce here an epistemological reconstruction for understanding the construction (or rather, reconstruction) of physical quantities. Our approach introduces quantities as part of the networks of other quantities and laws, where quantifying experiments are seen as having a central role in building up the network and in determining its structure. As an application, we discuss the (re)construction of temperature as a measurable quantity. This quantity was selected for the present case study for several reasons. Temperature is one of those physical quantities which is used daily. It is easily measured using thermometers and thus we see its measurement as quite unproblematic. Nevertheless, this simple concept seems to pose many learning difficulties for university students (cf. Carlton 2000; Taber 2000; Cotignola et al. 2002; Meltzer 2004). Moreover, textbooks quite often connect temperature straightforwardly to the average kinetic energy of particles, and so they reduce temperature to mechanical quantities and ‘explain’ it through the microscopic atomic model. This, however, does not help in understanding how, after all, temperature as a macroscopic concept and quantity is formed. Moreover, this ‘reduction’ too easily leads to the oversimplified ideas of temperature devoid of macroscopically meaningful content (cf.