Teaching
about energy
There is no shortage of different approaches
to the teaching of energy and this has
resulted in much confusion and conflicting
advice. These resources are intended
to promote a consistent approach.
The key ideas about energy that are
developed are:
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how
energy is stored |
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|
how energy
is transferred |
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conservation
of energy |
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|
dissipation
of energy |
These ideas are explored in a series
of booklets that have been grouped into
these three sections:
Click on the section titles to access
the booklets.
What
is energy?
Many school textbooks introduce
energy by stating that it is difficult
to say exactly what it is. This is a
very reasonable place to start, since
there is no easy answer to the question
‘What is energy?’ There
are formal definitions, but these don’t
really help students to understand what
it is. It may be better to think of
understanding energy as coming to know
the character in a drama or a novel
– getting to know the concept
bit by bit as more of the story about
its characteristics unfold.
There are at least three broad ways
to think about the nature of energy.
Energy
as a value. One way of thinking
of energy is simply as a value that
can be calculated. For any process you
can, in principle, calculate the total
energy before and find that it is the
same as the total energy after. We could
think of this as a ‘book-keeping’
approach.
Energy in many guises. Hot things
are seen as having ‘heat energy’,
moving things as having ‘kinetic
energy’, and so on. Energy can
change itself from one such ‘guise’
to another – for example, when
a fuel burns, ‘chemical energy’
is changed into ‘heat energy’.
But little understanding is gained by
naming ‘forms of energy’.
It becomes just a classification game
for its own sake.
Energy is energy. A third approach
is to think of energy as ‘fluid-like'
– and the same kind of thing whether
it is in a hot object or a moving one.
It doesn’t change its nature but
its location, perhaps becoming more
concentrated in one region, or more
spread out. Though the ‘energy
as a value’ interpretation is
entirely valid at appropriate levels,
it is this third approach to energy
that is promoted in these resources.
Transforming
or transferring?
A very common way to introduce energy
in KS3 has been the ‘forms of
energy’ approach. A central feature
of this approach has usually been the
‘energy circus’, in which
a wide variety of phenomena are used
to illustrate the many different kinds
of ‘energy transformation’.
However, the first version of the National
Curriculum, and every version since,
omitted any references to ‘forms
of energy’ or ‘energy transformation’
and instead focused on the processes
of ‘energy transfer’. The
implication was that there should be
a move away from thinking about energy
as ‘changing from one form to
another’ and to think of it as
staying ‘the same kind of thing’,
with the focus on where it is stored
and how it goes from one place to another.
There is a concern that much of the
talk involving forms of energy is just
adding ‘verbal ornamentation’
to descriptions of changes. When you
switch on a light in a room, the electrical
current makes the lamp produce light.
What deeper understanding is gained
by calling this a change of electrical
energy to light energy? In addition,
students do not always find it easy
to use the ‘correct’ labels
to attach to these energy changes and
often invent their own. So, a child
taking part in a race might be seen
as converting ‘food energy to
running energy’. Textbooks, as
well as children, also show variations
in the terms used for ‘forms of
energy’, which complicates things
further.
Some would go so far as to say that
the use of ‘forms of energy’
actually undermines the coherence of
the energy concept, and this coherence
across the physical world is its greatest
strength.
It was these difficulties that led the
National Curriculum to refer throughout
to ‘energy transfers’. While
the change in terminology from ‘transformation’
to ‘transfer’ seems slight,
it actually signifies a fundamental
change. Talking about energy transfer
stresses the importance of thinking
about energy as staying the same kind
of thing but in going from place to
place.
Often, however, the significance of
the new terminology has gone unnoticed,
with the term ‘transfer’
substituted for ‘transformation’.
It is common to see phrases such as
‘chemical energy transferred to
heat energy’. When you think about
it the word ‘transfer’ makes
no sense in this context.
Stores
and transfers
Energy can be stored in different ways,
so a secondary question is to ask what
kind of stores are involved. Examples
of different kinds of energy store are:
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thermal |
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kinetic |
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elastic |
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gravitational |
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electrical |
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chemical |
Because ‘energy is energy’
it does not change from one form to
another – rather it can be transferred
from one kind of store to another. This
means that instead of talking about,
for example, thermal energy, it is more
helpful to talk about a thermal store
of energy.
Energy can move from one store to another
in various different ways. For example,
energy is transferred from the engine
to the wheels of a car through a series
of gears and shafts; energy can be transferred
from a battery to a lamp using an electrical
circuit.
Examples of ways of describing
transfer of energy are:
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by
heating |
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mechanically |
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electrically |
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by radiation |
Classification of transfer processes
can be more problematic than sorting
energy stores. The rules are not so
clear, and these resources avoid such
classification.
Conservation
and dissipation of energy
The ‘book-keeping’ approach
to energy is based on the ‘conservation’.
Indeed, the observation that energy
is conserved, unchanged in quantity,
in all processes makes it a very important
concept. An understanding that energy
transfers from one place or system to
another whilst neither increasing or
decreasing, is of key importance. For
this, students need to develop ideas
about stores of energy and also about
energy dissipation, which is the spread
of energy from a store into wider surroundings
so that it is so diluted as to be undetectable.
The key point here is that ‘spread’
does not mean the same as ‘ceasing
to exist’. |
