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When a solid metal is heated, do the atoms expand? What kind of question is this?

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I was rather puzzled recently by two text book particle diagrams on opposite pages. On the left hand page were particles depicted as solid balls touching, so show how the metal is almost incompressible, and a fixed shape. On the right hand page, the atoms were a little way apart, with extra lines to indicate movement, as the heated metal expands slightly and the vibrating atoms push each other apart. Could the atoms be touching, yet slightly apart? As I searched the scientific literature, I began to think this was a philosophical question, about the nature of modelling, and about the nature of science. We chose to explore this dilemma with a group of 17 year old physics students in a school in Malta, through discussions about explaining both thermal expansion and thermal contraction. Our evidence comes from written explanations provided by the students, and their conversations in class recorded in class by their physics teacher (JBM) over a period of one month as we posed contradictory evidence to see how their theories changed. What came out were typical characteristics of resistant to change, even in a strong case of cognitive dissonance. The seminar links theoretical research with a case study of how it plays out in a class of learners.

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