New trends in physics teaching, v.4; The ... - unesdoc - Unesco

Hungary
between two bodies only. Building a physics teaching programme on interactions cannot hide
the fact that, in addition to the common materials which are apparently impenetrable and
certainly touchable, there is also ‘action at a distance’. The texts therefore go on to consider the
magnetic, electric and gravitational fields.
Because it is easy for the pupils to perform experiments with magnets, it is the magnetic field
which is used to introduce the concept of field. The pupils make simple experiments with bar
magnets and pieces of iron, noticing that the magnet can change, for example, the position and
the motion of the piece of iron. This occurs without contact. We suggest to the pupils that the
magnet is surrounded by a special environment which interacts with pieces of iron within it.
We call this special environment a magnetic field. And we can recognize it only by its effects. The
state of the magnetic field changes during its interaction with the piece of iron. This can be
shown by the behaviour of iron filings when a piece of iron is moved through a field. The iron is
rather like a handle with which the field can be changed. These experiences lead us to say that
magnetic attraction and repulsion are the results of the interaction between a magnetic field and
magnetized material.
The concept of the electric field is similarly developed using a number of experiments. But the
gravitational field and gravitational interaction are taught without experiment, relying on the
analogy of the magnetic and the electric fields. To quote from the textbook: ‘The change in
motion of a freely falling body can be explained by a field surrounding the Earth. This field is
called a gravitational field. Its existence can be deduced only from its effects. The gravitational
field interacts with all matter independently of its material. And the result is always an attraction’
[ 121. As can be seen, fields are introduced as possible partners in interactions and it is shown
that, as in body-body interactions, body-field interactions change the states of both partners.
Introduction to energy
At this level, the concept of energy is developed over a series of lessons in which the pupils are
systematically introduced to the idea. The starting point is the ability to produce change in the
warmth of a body (‘warming capability’). It wil be noticed that this may differ in amount.
The measure characterizing the ‘warming capability’ of a body is called energy. Bodies having
excess energy may cause many kinds of change in other bodies. Energy, then, is a measure of the
changing ‘warming capability’ of a body. This is a general, but qualitative ‘energy definition’. On
the basis of their experiments the pupils recognize that, in an interaction, the energy of one
partner increases while the energy of the other decreases. Such experiments allow us to introduce
the idea of the conservation of energy.
The next concept to be studied is that of ‘work’. Work is an energy change which comes about
through the action of a force producing motion. Fields, too, have the ability to produce change
and must also possess energy.
Having learnt about the corpuscular structure of matter, the pupils are ready to recognize a
corpuscular interpretation of internal energy. Heat wil be described as an internal energy change
which takes place during thermal interactions. When the pupils formulate in words that energy
changes can come about through the performance of work and by thermal interaction, they are
making a statement of the first law of thermodynamics.
It must be emphasized that the textbook speaks of energy as a measure of the ability of a body
or of a field to act in certain ways. Thus energy is not presented as an existing, objective reality
or its property. Pupils appreciate it as a physical concept which characterizes a capability; i.e. the
ability for change of an objective, existing reality.
109