Models in physical sciences (Part I): A nice-to-have or something else?

Inclusions of the nature of science (NOS) in science curricula have been deemed essential to science teaching and learning, with arguments ranging from enhancing understanding of concepts to an appreciation of the scientific enterprise or simply for scientific literacy.

But research assessing the treatment of NOS in schools and science textbooks reveals bleak results that do no favours to science or to its teaching. Textbook authors have been accused of having inadequate understanding of NOS and of having the tendency not to consult and incorporate relevant, let alone modern scholarship. And this surely affects, if not reflecting, notions of NOS of the wider educational community that sees textbooks as authoritative documents.


NOS out there….

And so here we go….. based on what we find in South African textbooks, the two most common aspects of NOS talked about in schooling must be a) the tentative nature of science and b) notions of what science models and theories are. Excerpts 1 to 6 below reflect the norm communicated to teachers and learners out there.

Can you spot the problems in excerpts 5 and 6?


What is wrong with these excerpts?

Excerpt 1, suggests that a science theory is no more than ‘TALL STORIES’ that should be taken with a pinch of salt (as in the everyday meaning of ‘theory’). This is in stark contrast with the consensus view among science educators, scientists and philosophers of science for whom a scientific theory is a well-established, highly substantiated, internally consistent system of explanations.

Excerpt 2 advises on how to ‘tell’ a scientific model from other models by following word-clues!

Excerpt 4 communicates the “tentative nature of science” as a series of changes to a model until we finally arrive at the TRUTH and the PROPER understanding of something, of the atom in this case. Same applies to excerpt 1, “… more than just a theory”, implying that the theory is by now reality.

All excerpts imply that science models are somehow feeble simplifications of reality and so, not well founded. They help us visualise real ‘things’ that we cannot see because they are either too small or too complex. So according to these ideas, the ‘things’ of the micro-cosmos, like atoms, electrons and other particles, are real and exist and we know their behaviours, and our task as teachers is to model them in a simplified way for children to visualise. Authors that communicate such ideas never seem to question “How have we come to know about those ‘things’ in the first place? How do we know about their behaviours?”

It has been suggested that the notion of a science model as a copy of reality, may be held predominantly by teachers with a biology background, who are the majority and who often teach and write about physical sciences. Such teachers had exposure to replicas of the human skeleton, lungs, etc. referred to as models. The notion of ‘model’ in biological disciplines interferes with the notion of a ‘model’ as it is expected to be understood in the physical sciences. This also means that they have not been exposed appropriately to aspects of the nature of science during their studies, and this should then apply to science teachers in general. Experience suggests that any student teacher sees NOS as a load of mumbo-jumbo, done generically as a small part of a methodology course by lecturers who perhaps don’t understand it themselves….

What is a ‘model’ in science?

How scientific knowledge is constructed is a story of its own. But, we can say that a science model is a product of the imagination of the scientist, a mental construct of inferred entities (i.e. imaginary) that behave in particular ways assigned by the scientist (we call these assumptions).  A science model is constructed to EXPLAIN how real-world phenomena come to be and it should also PREDICT successfully outcomes of future phenomena or else it may be discarded. The inferred entities of science models do not look and do not behave like the entities of the real world they are meant to explain.

For example, the particles of a gas in the kinetic theory of gases, which are the inferred entities, do not behave like the gas itself, which is the real entity. And yet, we use the actions of the inferred entities (i.e. particles) to explain the macroscopic properties of the gas. For instance, we explain the pressure of a gas (a macroscopic property /real phenomenon) by imagining collisions of particles with the walls of the container (behaviour of inferred entities). And this is how we explain the origin of pressure in gases; this is a scientific explanation. If we decrease the volume of the gas container, leaving other parameters unchanged, the kinetic theory predicts that the pressure of the gas should increase, because the gas particles come closer together and collide more often with the container walls. And indeed in the real world the pressure of the gas increases if we decrease its volume. The kinetic theory has predicting power.

On models, explanations, knowns and unknowns…

Do not be fooled into thinking that it’s a simple matter to produce a science model. Scientists do not use wishful thinking. There is a lot of thought and effort, minds and trials involved over time in their construction and they always remain under construction. Models must measure up against reality and must adapt in order to explain and predict a variety of phenomena. The atomic model and the kinetic model of matter are such powerful models. And note that not all theories/models deal with a “micro-cosmos”. In physics we use wave models, models of the universe, models of black holes, even in kinematics when we describe the motion of a car we actually use a model! Perhaps it’s safe to say that “where there is an explanation there is a model….”


So, an explanation in science is to select an appropriate model and tell the story of how its inferred entities have acted to produce a certain phenomenon. The scientific model is the known (since we have constructed it) the real phenomenon to be explained is the unknown. Some may find paradoxical that the real phenomenon is the unknown since it is often most familiar, like rubbing a ruler and picking up bits of paper. But familiar does not mean understandable. We want to explain why the ruler picks up bits of paper. We cannot explain this just because we have seen the ruler many times! We have to imagine what might be happening inside the ruler and the paper. In doing so we produce a model. Fortunately, scientists have already done this job for us and have produced powerful models, tried and tested, that we can use to explain and predict. This is the notion of ‘science model’ that is essential in physical sciences.

In the excerpts from the textbooks, we have seen that the notion of science models as products of science and means to explanations is missing! The inferred nature of the entities of science models, which is another aspect of NOS, seems unheard of! Speaking of unknowns! Creativity and imagination in the construction of scientific knowledge are not given much credit. And yes, in the teaching of physical sciences this omission has CONSEQUENCES …..


To be continued…..



[1]   Siyavula “Grade 10 Physical Science”, Version 0.5, 2010 NCS, p.38, on the Kinetic Theory of Matter

[2]  “Oxford Successful Physical Sciences Grade 10 Learner’s Book”, Oxford University Press Southern Africa (Pty) Ltd 2011, 1st publ. 2007, 2nd ed. 2011, 10th impress. 2013

[3]  Siyavula “Grade 10 Physical Sciences”, Version 1 CAPS, DoBE, p. 62

[4]  “Oxford Successful Physical Sciences Grade 10 Learner’s Book”, Oxford University Press Southern Africa (Pty) Ltd 2011, 1st publ. 2007, 2nd ed. 2011, 10th impress. 2013, p. 9

[5]  Siyavula “Grade 10 Physical Sciences”, Version 1 CAPS, DoBE, p. 62




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