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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.
This unit deals with two major problems of understanding relating to energy (Can we use energy up? Do Fuels contain energy?) a few minor conceptual issues, and then looks at the environmental impact of our energy ‘use’.
Download 1.1: 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.
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 download 1.1
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 1.1 suggesting that energy is a substance that can be
used up.
i) Energy itself is not used up or destroyed but it gradually degrades to waste heat as it makes things happen.
ii) Energy is not a substance contained within fuels or food. When energy is transferred, fuels and food need to combine with oxygen during burning or respiration.
(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 is the Sun. High grade sunlight, dangerous to the skin, provides the power source for plants and life and for the weather systems and climate. Through 'use' its energy becomes degraded to low grade heat energy, and 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 fuels made millions of years ago with oxygen, and these are not replenished (often called non-renewable energy resources).
Download 2.2 Can we use energy up?
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 1.1 answers this using a 'Sankey' diagram (same as slide 6 in download 1.1). 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 go back to your body and respire some more food and oxygen and wind it up all over again.
Download 2.3 Sankey diagrams
2.4 Fuel-Oxygen Systems (KS 3 & 4)
We all say that food contains energy, but this shorthand expression leads to a serious misunderstanding about how the environment works. The PowerPoint slides (7 - 29) rehearse this argument (see especially the notes pages attached to each slide) and this download will also help.
Download 2.4 Fuels don’t contain energy
Download 3.5 has a number of questions that explore possible misconceptions about heat and temperature. It also contains a commentary.
Download 2.5 Questions on heat and temperature
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.
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.
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.
This is 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.
- Ten watt speakers are not as loud as twenty watt speakers, and so on.
They 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.
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, so here’s one more:
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 fingers together flat down on the wooden tabletops, whilst you explain: “Notice that the table top begins to feel warm. When I say I want 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 you 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 when we touch the ‘cold’ object the heat is conducted away and it remains cold.
Downloads in this Unit:
Section Developed by:
Keith Ross, University of Gloucestershire
May 2005
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