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  5. K4.5 Energy Resources and energy transfer

K4.5 Energy Resources and energy transfer

Abstract

Energy is one of the central concepts of the science curriculum and is used somewhere in virtually every topic studied although the concept is rarely used consistently by pupils (and teachers or tutors). This article explores the development of the 'energy' concept and some of the barriers to its understanding. In particular the idea of dealing with 'energy transfer' rather than 'types of energy' is stressed since many trainees (and most tutors) have themselves been taught and well drilled in the latter approach. The potential confusion between 'heat' and 'temperature' is explored. Stress is placed on the ideas of degradability of energy (and the recycling of matter) together with the distinction between renewable and non-renewable energy sources. There are a number of downloads that provide teaching material that can be adapted for use with trainees and practical experiences useful to support the understandings of learners generally.

This is one of 17 articles whose main aim is to support the processes of teaching/learning between the science education tutor and the trainee science teachers with a focus on “teachers’ knowledge and understanding”. During a primary or secondary BEd, PGCE or GTP we hope that those learning to become science teachers will be able to challenge their own understanding of science and scientific concepts. Unit K0 specifically explores general issues relating to all the knowledge units - to the learning of science.

Standards: This unit specifically addresses Q14 but, appropriately used can contribute to and provide evidence of competence for many others of the standards especially Q4,6,7,8,18, 22 and 25.

Keywords: Energy, Energy transfer; conservation; degredation, Heat, Temperature.

Contents

1.0 Introduction - What is energy?
2.0 Conceptual Barriers to understanding energy
2.1  Being energetic (KS1 and 2)
2.2  Fuelling life, Climate and technology (KS3 & 4)
2.3  Energy transfer (KS 1-4)
2.4  Fuel-Oxygen Systems (KS 3 & 4)
2.5  Heat and temperature (KS1-3)
3.0 Progression in children's ideas
4.0 Giving Practical experiences
5.0 Useful references
6.0 Useful websites

1.0 Introduction - What is energy?

The concepts of energy and energy change are all-embracing ideas which tie together all topics in science. Although not specifically mentioned in the National Curriculum for Key Stages 1 and 2, energy is a word that is known to most children before they come to school. It used to be an attainment target in the 1989 version of the National Curriculum and was a strand of Sc4 in the 1991 version. It underlies all physical processes - sound, light, electricity, movement, heat. It drives living things within ecosystems and causes changes in materials or is released by their reactions.

What people actually understand by the word energy varies tremendously, and the range of confusions associated with it are examined below. It is this tremendous variation of usage that frightened the authors of the Curriculum 1995 Orders into omitting it from the primary curriculum. Our opinion is that it is of such central importance that its meanings must be clarified so children can begin to use the word in consistent and useful ways. Having said this we must also expect teachers and ‘experts’ as well as students to make mistakes, or interpret things in different ways. Our discussions about energy require considerable amounts of ‘clarification’ and ‘negotiation’.

This unit deals with two major problems of understanding relating to energy (Can we use energy up? Do Fuels contain energy?). This is followed by a few minor conceptual issues, and the environmental impact of our energy ‘use’ is explored.

Download 1.0a: Subject Knowledge Energy - PowerPoint summarises all these issues. Please refer to the notes pages in the presentation for help in using the PowerPoint with students. It has been used, in a simplified format, for Primary, and can be used in full for Secondary trainees.

Download K4.5_1.0a 'Energy'

This is a useful quote from the Science Museum web page:

When it comes to teaching about energy some textbooks adopt the transformation model, which has at its core the notion of 'types of energy'. The terminology associated with this approach includes common phrases such as 'heat energy' and 'electrical energy' which, although useful in helping to cover some of the basics, are no longer viewed as strictly correct.
A better approach to teaching about energy can be found in the transference model, which carefully avoids any mention of types of energy. Instead, the transference model accepts that energy simply is, and that it can be transferred, stored, conserved or dissipated. This is the approach now recommended by most science educators in the UK, including the Nuffield Curriculum Centre, the Institute of Physics and the chief science and technology consultant to the QCA.

We shall attempt to follow this transference convention in this unit. At this URL, along with several other useful resources, is a short PowerPoint entitled: Alternative models for teaching energy at Key Stage 3 from Nottingham LEA which clarifies the two approaches.

2.0 Conceptual Barriers to understanding energy

Trainees, like pupils in school, need to be challenged with questions that elicit their personal ideas about energy so any misconceptions can be addressed. The paragraphs that follow are all based on areas that have confused children and students alike. Further details can be found in the PowerPoint presentation, download 1.0a mentioned above.

2.1 Being energetic (KS1 and 2)

Many children associate energy with 'being energetic' - they can say that to get energy you must exercise, or they may say that doing exercise makes you tired so you lose energy. 

  • What are the grains of truth in these two contradictory statements? 

Children often first hear the word energy in relation to themselves: 
You are very energetic today.
You've used up all your energy.
Keep exercising to build up your energy.
This leads to a general understanding of energy as associated with movement. Building up your energy really means strengthening or building up your muscles. 

The expression 'using up energy' leads to the two major misconceptions in download 1.0a suggesting that energy is a substance that can be used up. 

i) Energy itself is not used up or destroyed but as it is ‘used’ to make things happen it gradually degrades to waste heat. Thus ‘high grade’ energy, such as sunlight or electrical energy, can be made to do useful things (such as power life, or our vacuum cleaner) as it transforms to less useful forms of energy, ultimately ending as waste heat. The energy is still there but in a useless form. (note our use here of the transform approach to talking about energy change). We might also say that energy transfers from where it is concentrated and useful to the surroundings where is it spread out and useless.

ii) Energy is not a substance contained within fuels or food. To obtain energy from fuel or food they need to combine with oxygen during burning or respiration. The energy stored in the chemical system is transferred to useful work and to the surroundings (waste heat).

2.2 Fuelling life, Climate and technology (KS3 & 4)

(High grade) energy is needed to make things happen. It is central to all life and activity. The Earth and its systems are largely fuelled by the (high grade) visible light from the Sun. 

Here is a question to think about:
Explain why a water wheel, a wind mill, a horse drawn plough, a sailing boat, and someone cycling are all fuelled by replenishable 'solar' energy; and why a coal-fired power station, a tractor, a motor boat and a motor bike are all fuelled by non-replenishable 'solar' energy. 

And here is a response:
Rooms get spontaneously untidy. You have to expend energy to get them tidy, in which case the energy becomes scattered as the things in the room become ordered. This is the law of entropy, the second law of thermodynamics, which says that every change leads to disorder - either of the system or of its surroundings (or both). It is common experience - we all know that things get spread out over time. Usually it is high grade energy that degrades to waste heat as matter is cycled. 

The dominant energy source for all changes we experience on Earth is the Sun. High grade sunlight, dangerous to the skin, provides the power source for plants and life (a horse drawn plough and someone cycling) and for the weather systems and climate (a water wheel, a wind mill and a sailing boat). Through 'use' (or merely by warming soil, rock, water etc.) its energy becomes degraded to low grade heat energy, and most of this waste heat is radiated back out to space. We have a fixed amount of matter on this planet which is (re)cycled (by life, climate or technology) whilst it is energy that spreads out over time. Daily sunlight is a replenishable source, but when we use fossil fuels we are combining oxygen with fuels made millions of years ago from the action of sunlight on plants, and these fuels are not replenished (often called non-renewable energy resources).

Download K4.5_2.2a 'Can we use energy up?'

2.3 Energy transfer (KS 1-4)

Consider a person winding up a clockwork train and making it run along the floor. Account for the energy transfers from winding up to when the train has finally stopped.

Questions such as this abound in energy topics at all ages. Download 2.3a answers this using a 'Sankey' diagram (same as slide 6 in download 1.0a). Note that, although there is no loss of energy (it ends up as waste heat), the usefulness of the energy is gone by the end. To make the train go again you cannot use the waste heat - you have to use your body and respire some more food and oxygen and wind the train up all over again. 

Download K4.5_2.3a 'Sankey diagrams'

2.4 Fuel-Oxygen Systems (KS 3 & 4)

Most people are happy to say that 'food contains energy', but this shorthand expression leads to a serious misunderstanding about how the environment works. The PowerPoint slides (7 - 29) in download 1.0a rehearse this argument (see especially the notes pages attached to each slide) and this download will also help.

Briefly, energy is stored when sunlight acts on carbon dioxide and water in plants to form plant material (which becomes our food) and oxygen. We obtain energy by respiration of that food, in which the oxygen (a reactive dangerous gas) rejoins with the food. Energy is stored in the food-oxygen system, not in the food alone. This download explains it in full:
Download K4.5_2.4a 'Fuels don't contain energy'

2.5 Heat and temperature (KS1-3)

Download 2.5 has a number of questions that explore possible misconceptions about heat and temperature. It also contains a commentary on why the misconceptions might occur. Briefly: heat is measured in joules and is energy, but temperature tells you how hot something is. A red hot nail is very hot but has very little heat energy in it. A kettle of boiling water is not so hot but needs far more energy to make it hot.
Download K4.5_2.5a 'ideas about heat and temperature'

3.0 Progression in children's ideas

The following is based on research on children's ideas and covers several themes of the Science National Curriculum even though the word energy itself is not actually mentioned either at KS1 or at KS2.

Foundation Stage and Key Stage 1
Young children will hear the word energetic, and associate it with being active. They will begin to associate eating food with getting energy, though they are unlikely to make the important link with air at this stage. The idea that anything that moves has energy (eg a car) begins to make sense to these children, but it is less likely that they will generalise further. Their ideas of heat and temperature will focus on themselves as a reference point. They may say metals are 'cold', and blankets are warm - ideas which lead to misconceptions later. When hearing the word temperature they may think of 'having a temperature' rather than realise it is a measure of how hot or cold something is. They are unlikely to associate light and sound with energy, though they will begin to realise that the creation of loud sounds and bright lights needs a lot of energy.

Key Stage 2 
The broadening of the energy concept probably comes through studying electricity - children realise that it can make lots of things happen, and begin to see electricity as a source of energy. That means that the movement of an electric motor, the light emitted from an electric light, the heat from a kettle, and the sound from a loudspeaker must all be 'types' or 'forms' of energy. Finally the idea that this movement, light etc can be produced in other ways, such as through burning coal or a candle, shows that energy can be stored and ‘used’. It is at this stage that the unhelpful idea develops that fuels contain energy, and therefore that fuels and food must be 'made partly of energy'. They will say (as most people do) that food contains energy, rather than we get energy from respiring food and air. In the same way they are unlikely to realise the need for air during combustion of fuels, and therefore unlikely to realise how massive the exhaust gases are in relation to the fuel used. 

Although children see energy changing 'form' they almost universally say that energy gets 'used up'. In this way they are using the word energy to mean what scientists would describe as 'high grade, useful forms of energy', such as the daily ration of sunlight the Earth receives. It is encouraging* to remember that most of this incoming solar energy ‘just warms things up’ or is reflected away, and only about 1% of the energy is ‘trapped’ by photosynthesis. ‘Just warming things up’ also drives the weather systems and much of the oceans’ currents on Earth, however there is still plenty of ‘spare’ capacity for making use of this renewable energy resource. (*because there is still plenty for us to use to replace our reliance on fossil fuels.)

Key Stage 3 
Children begin to appreciate the difference between heat and temperature. They may still think that a blanket has its own warmth, rather then being an insulator that prevents heat energy from flowing, and might say that ice wrapped in a blanket will melt faster than unwrapped ice, as indeed many much older people might also say. They will begin to realise that sunlight drives life and weather systems on Earth, and that humans have freed themselves from relying on this daily source by burning fossil fuels, but not without some serious consequence for life and climate. They begin to develop the concept of energy measured in joules - energy which cannot be used up and so becomes scattered as waste environmental heat, to be radiated out to space at a rate that keeps the temperature of the Earth roughly in balance as follows:

For a constant average global temperature:
Energy radiated out (mostly as IR) = (Energy received from sun, mostly as visible light) + (Energy from Earth’s interior, mostly conducted up to the surface, but occasionally in a more violent fashion!) + (Energy from man’s use of fossil fuels)

The last of these is tiny, though the waste gas, carbon dioxide, from the process, builds up in our atmosphere making it harder for the IR (heat energy) to be radiated away, requiring a higher average surface temperature to restore this balance, experienced as global warming.

Ideas about energy are most easily grasped in terms of power. For example: 

  • A 1 kilowatt fire gives out 1 kilojoule of heat a second. 
  • A 3 kw kettle boils water twice as fast as a 1.5 kw kettle. 
  • A 100 watt light bulb is twice as bright as a similar 50 watt bulb (and in the same way an 8 watt 'low energy' light bulb is twice as bright as a 16 watt bulb). 
  • Ten watt speakers are not as loud as twenty watt speakers, and so on. Children begin to appreciate the idea of energy degradation to explain why energy appears to be used up, even though the joules are still there.

Key Stage 4
As the measurement of energy changes becomes more prominent in the lessons we have to be careful not to let the energy concepts become obscured. We need to continue to make a clear distinction between the useful energy that drives systems and thereby becomes degraded to waste heat, and the idea that energy, measured in joules, does not get used up. We also need to make it clear that when people talk about energy resources they are often actually talking about fuel reserves. The distinction between matter (such as fossil fuel) and energy (such as is stored in systems such as ‘Earth/water’ and ‘fuel/oxygen’) must remain clear.

4.0 Giving Practical experiences

There are several practical activities mentioned in the downloads above that will be valuable for trainee teacher to experience first hand for themselves. These first hand experiences are so important - here’s one more:

'Cold' metals/'warm' blankets

People often say that metals are cold and blankets are warm, yet, in a room, they should both be at the same temperature. How can we sort this problem out?

Ask your trainees to place their hands (with fingers together) flat down on the wooden tabletops, whilst you explain: “Notice that the table top begins to feel warm. In a moment I will ask you to move your hand to a fresh place on the tabletop, and then more it back to exactly where it was before. I want you to notice how warm or cold the table feels. OK move your hand now.” Students will notice that the fresh tabletop is cold but the place where they have been touching is warm. Their hands have actually made the table warm. The same thing happens with a pair of gloves – the warmth from your hand warms up the inside of the glove and make the glove warm. Because the wood of the table and the fabric of the glove are not good conductors of heat energy the heat stays in one place making the object warm. However if you touch a metal object the heat is conducted away so quickly that in order to make it feel warm you will have to warm up the whole object, not just the surface where you touch. A small metal object such as a coin, however, quickly warms through when you handle it.

Thus when we say metals are cold and blankets are warm – there is a very big grain of truth in this – as soon as we touch the ‘warm’ object we make its surface warm (but the inside remains cold), but when we touch the ‘cold’ object the heat is conducted away from the surface and the surface remains cold (actually the whole object becomes just a little warmer, so if the object is small, like a metal coin, it soon heats up to body temperature).

5. Useful references

  • Colin Kruger, Mike Summers, Jenny Mant, Ann Childs, Jane McNicholl (1998) PSTS Pack 8 Teaching Energy and Energy Efficiency ASE Booksales ISBN: 0903535483 These teacher education materials, produced by the Primary School Teachers and Science (PSTS) Project, are designed to help primary teachers develop their knowledge and understanding of concepts in a number of subject areas.
  • Mike Summers, Anne Childs, Graham Corney, Colin Kruger & Jenny Mant (2002) Teaching Sustainable Development in Primary Schools ASE Booksales ISBN: 0863573363 
  • Brian Smith (2004) The Science You Need To Know ASE ISBN 0863574009 Now available from ASE Booksales, this reference source is for teachers in primary schools who may not be science specialists. Written by Brian Smith and edited by Valerie Wood-Robinson, it provides far more information on the science background than is actually needed at Key Stages 1 and 2, so offering readers an overview of the context of what they are teaching and better preparing the learners for Key Stage 3 and beyond.
  • Sang, D. (ed.) (1999) Teaching Secondary Physics John Murray ISBN: 0719576369 
    This is an extremely helpful book, with chapters on all the ‘physics’ topics, including, especially, chapter 4 on Energy http://www.hoddereducation.co.uk
  • Ross, K. (2000) Energy and Fuels, Chapter 6 in Littledyke, M., Ross, K. and Lakin, L. (2000) Science Knowledge and the Environment London: David Fulton ISBN: 1-85346-625-56. 

6. Useful websites

There is a huge resource out there, just waiting to be explored. Here are some of the standard ones:

  • DfES standards site: http://www.standards.dfes.gov.uk/schemes2/secondary_science/sci07i/
  • This is an old site but with some useful links: http://atschool.eduweb.co.uk/trinity/energy3.html 
  • The Science Museum: http://www.sciencemuseum.org.uk/exhibitions/energy/site/TeachersTopTips.asp
  • And here is a useful site from Nottingham LEA: http://www.nottinghamschools.co.uk/eduweb/schools/schools-template.aspx?id=873

Section Developed by: Keith Ross, University of Gloucestershire Nov 2005

Published: 23 Nov 2005, Last Updated: 23 Sep 2008