Getting a group of British physics teachers to agree to a new consensus is like herding cats: much easier in principle than in practice.
However, it seems to be me that, generally speaking, the IoP (Institute of Physics) has persuaded a critical mass of physics teachers that their ‘Energy Stores and Pathways’ model is indeed a Good Thing.
It very much helps, of course, that all the examination boards have committed to using the language of the Energy Stores and Pathways model. This means that the vast majority of physics education resources (textbooks and revision guides and so on) now use it as well — or at least, the physics sections do.
Energy Stores and Pathways: a very brief overview
There’s a bit more to the new model than adding the word ‘store’ to energy labels so that ‘kinetic energy’ becomes ‘kinetic energy store’; although, truth be told, that’s not a bad start.
I have banged on about this model many times before (see the link here) so I won’t go into detail now. For now, I suggest that we stick with the First Rule of the IoP Energy Club….
You can also read the IoP’s own introduction to the Energy Stores and Pathways model (see link here).
The Problem with Photosynthesis
The problem with photosynthesis is that it is often described in terms of ‘light energy’. The IoP Energy Stores and Pathways model does not recognise ‘light’ as an energy store because it does not persist over a significant period of time in a single well-defined location. Rather, light is classified as an ‘energy carrier’ or pathway (see also this link)
It is possible that the problem is simply one of resource authors using familiar but outdated language. It would seem that exam board specifications are punctilious in avoiding the term ‘light energy’; for example, see below.
How to describe Photosynthesis using the Energy Stores and Pathways model
It’s very simple: just say ‘plants absorb the energy carried by light’ rather than ‘plants absorb light energy’.
In diagram form, the difference can represented as follows:
Over time, I think that the vast majority of physics teachers (in at least in the UK) have come to see the value of the ESP (Energy Stores and Pathways) approach.
I this that I speak for most physics teachers when we hope that biology and chemistry teachers will come to the same conclusion.
H’mmm…if navigating physics teachers towards a consensus is like herding cats, then to what can we liken doing the same for a combined group of physics, biology and chemistry teachers? Perhaps herding a conglomeration of cats, dogs and gerbils across the boundless, storm-wracked prairies of Tornado Alley. In the dark. With both hands tied behind your back.
The AQA GCSE Science specification calls for students to understand and apply the concepts of not only thermal energy stores but also internal energy. What follows is my understanding of the distinction between the two, which I hope will be of use to all science teachers.
My own understanding of this topic has undergone some changes thanks to some fascinating (and ongoing) discussions via EduTwitter.
What I suggest is that we look at the phenomena in question through two lenses:
a macroscopic lens, where we focus on things we can sense and measure directly in the laboratory
a microscopic lens, where we focus on using the particle model to explain phase changes such as melting and freezing.
Thermal Energy Through the Macroscopic Lens
The enojis for thermal energy stores (as suggested by the Institute of Physics) look like this (Note: ‘enoji’ = ‘energy’ + ’emoji’; and that the IoP do not use the term):
In many ways, they are an excellent representation. Firstly, energy is represented as a “quasi-material entity” in the form of an orange liquid which can be shifted between stores, so the enoji on the left could represent an aluminium block before it is heated, and the one on the right after it is heated. Secondly, it also attempts to make clear that the so-called forms of energy are labels added for human convenience and that energy is the same basic “stuff” whether it is in the thermal energy store or the kinetic energy store. Thirdly, it makes the link between kinetic theory and thermal energy stores explicit: the particles in a hot object are moving faster than the particles in the colder object.
However, I think the third point is not necessarily an advantage as I believe it will muddy the conceptual waters when it comes to talking about internal energy later on.
If I was a graphic designer working for the IoP these are the enojis I would present:
In other words, a change in the thermal energy store is always associated with a temperature change. To increase the temperature of an object, we need to shift energy into the thermal energy store. To cool an object, energy needs to be shifted out of the thermal energy store.
This has the advantage of focusing on the directly observable macroscopic properties of the system and is, I think, broadly in line with the approach suggested by the AQA specification.
Internal Energy Through the Microscopic Lens
Internal energy is the “hidden” energy of an object.
The “visible” energies associated with an object would include its kinetic energy store if it is moving, and its gravitational potential energy store if it is lifted above ground level. But there is also a deeper, macroscopically-invisible store of energy associated with the particles of which the object is composed.
To understand internal energy, we have to look through our microscopic lens.
The Oxford Dictionary of Physics (2015) defines internal energy as:
The total of the kinetic energies of the atoms and molecules of which a system consists and the potential energies associated with their mutual interactions. It does not include the kinetic and potential energies of the system as a whole nor their nuclear energies or other intra-atomic energies.
In other words, we can equate the internal energy to the sum of the kinetic energy of each individual particle added to the sum of the potential energy due to the forces between each particle. In the simple model below, the intermolecular forces between each particle are modelled as springs, so the potential energy can be thought as stretching and squashing the “springs”. (Note: try not to talk about “bonds” in this context as it annoys the hell out of chemists, some of whom have been known to kick like a mule when provoked!)
We can never measure or calculate the value of the absolute internal energy of a system in a particular state since energy will be shifting from kinetic energy stores to potential energy stores and vice versa moment-by-moment. What is a useful and significant quantity is the change in the internal energy, particularly when we are considering phase changes such as solid to liquid and so on.
This means that internal energy is not synonymous with thermal energy; rather, the thermal energy of a system can be taken as being a part (but not the whole) of the internal energy of the system.
As Rod Nave (2000) points out in his excellent web resource Hyperphysics, what we think of as the thermal energy store of a system (i.e. the sum of the translational kinetic energies of small point-like particles), is often an extremely small part of the total internal energy of the system.
My excellent Edu-tweeting colleague @PhysicsUK has pointed out that there is indeed a discrepancy between the equations presented by AQA in their specification and on the student equation sheet.
If a change in thermal energy is always associated with a change in temperature (macroscopic lens) then we should not use the term to describe the energy change associated with a change of state when there is no temperature change (microscopic lens).
@PhysicsUK reports that AQA have ‘fessed up to the mistake and intend to correct it in the near future. Sooner would be better than later, please, AQA!
Nave, R. (2000). HyperPhysics. Georgia State University, Department of Physics and Astronomy.
The first rule of IoP Energy Club is: you do not talk about energy . . .
. . . unless you’re gonna do a calculation.
— with apologies to Brad Pitt and Chuck Palahniuk
In the UK, the IoP (Institute of Physics) has developed a model of energy stores and energy pathways that has been adopted by all the exam boards. Although answers couched in terms of the old “forms of energy” model currently get full credit, this will almost certainly change over time (gradually or otherwise).
This post is intended to be a “one stop” resource for busy teachers, with suggestions for further reading.
Please note that I have no expertise or authority on the new model beyond that of a working teacher who has spent a fair amount of time researching, thinking about and discussing the issues. What follows is essentially my own take, “supplemented by the accounts of their friends and the learning of the Wise” (if I may borrow from Frodo Baggins!).
Part the First: “Why? For the love of God, why!?!”
The old forms of energy model was familiar and popular with students and teachers. It is still used by many textbooks and online resources. However, researchers have suggested that there are significant problems with this approach:
Students just learn a set of labels which adds little to their understanding (see Millar 2014 p.6).
The “forms of energy” approach focuses attention in the wrong place: it highlights the label, rather than the physical process. There is no difference between chemical energy and kinetic energy except the label, just as there is no difference between water stored in a cylindrical tank and a rectangular tank. (See Boohan 2014 p.12)
The new IoP Stores and Pathways model attempts to address these issues by limiting discussions of energy to situations where we might want to do calculations.
Essentially, the IoP wanted to simplify “energy-talk” and make it a better approximation of the way that professional scientists (especially physicists) actually use energy-concepts. The trick is to get away from the old and nebulous “naming of parts” approach to a newer, more streamlined version that is fit for purpose.
Part the Second: How many energy stores?
The second rule of IoP Energy Club is: youdo not talk about energy . . . . . . unless you’re gonna do a calculation.
— with apologies to Brad Pitt and Chuck Palahniuk
The IoP suggests eight named energy stores (listed below with the ones likely to be needed early in the teaching sequence listed first).
Many will be surprised to see that electrical energy, light energy and sound energy are not on this list: more on that later.
There are, I think, two very important points:
All of these energy stores represent quantities that are routinely measured in joules.
All of the energy stores represent a system where energy can be stored for an appreciable period of time.
For example, a rattling washing machine is not a good example of a vibration energy store as it does not persist over an extended period of time: as soon as the motor stops, the machine stops rattling. On the other hand, a struck tuning fork, a plucked guitar string or a bell hit with a hammer are good examples of vibration energy stores.
Similarly, a hot object is not a vibration energy store: it is better described as a thermal energy store. Thermal energy stores are useful when there is a change in temperature or a change in state.
Likewise, a lit up filament bulb is not a good example of a thermal energy store because it does not persist over an extended period of time; switch off the current, and the bulb filament would rapidly cool.
Note also that the electric-magnetic energy store applies to situations involving magnets and static electric charges. It is not equivalent to the old “electrical energy”.
The thread linking all the above examples is we limit discussions of energy to situations where we could perform calculations.
Thermal energy store is an appropriate concept for (say) the water in a kettle because we can calculate the change in the thermal energy store of the water and the result is useful in a wide range of situations. However the same is not true of a hot bulb filament as the change in the thermal energy store of the filament is not a useful quantity to calculate (at least in most circumstances). For further discussion, see this blog post and also this section of the IoP Supporting Physics website.
Part the third: How many energy pathways?
The third rule of IoP Energy Club is: there ain’t no such thing as ‘light energy’ (or ‘sound energy’ or ‘electrical energy’).
— with apologies to Brad Pitt and Chuck Palahniuk
In the new IoP Energy model, there is no such thing as a “light energy store”. Instead, we talk about energy pathways.
Energy pathways describe dynamic quantities that are routinely measured in watts. That is to say, they are dynamic or temporal in the sense that their measurement depends on time (watts = joules per second); energy stores are static or atemporal over a given period of time.
It is not useful to talk about a “light energy store” because it does not persist over time: the visible light emitted by (say) a street lamp is not static — it is not helpful to think of it as a static “box of joules”. Instead it is a dynamic “flow” of joules which means its most convenient unit of measurement is the watt.
As an analogy, think of an energy store as a container or tank; in contrast, think of a pathway as a channel or tap that allows energy to move from one store to another. )
You can read more on the “tanks and taps” analogy here.
The cautious reader should note that the IoP describe slightly different pathways which you can read about here. (Mechanical and Electrical Working are in, but the IoP talk about “Heating by particles” and “Heating by radiation”; on this categorisation, sound would fit into the “Mechanical Working” category!)
The fourth rule of IoP Energy Club is: I don’t care what you call it, if it’s measured in watts, it’s a pathway not an energy store, OK?
— with apologies to Brad Pitt and Chuck Palahniuk
You can look forward to more ‘IoP Energy Club Rules’, as and when I make them up.
Important note: all of the above content is the personal opinion of a private individual. It has not been approved or endorsed by the IoP.
Why do we make these analogies? It is not just to co-opt words but to co-opt their inferential machinery. Some deductions that apply to motion and space also apply nicely to possession, circumstances and time. That allows the deductive machinery for space to be borrowed for reasoning about other subjects. […] The mind couches abstract concepts in concrete terms.
— Steven Pinker, How The Mind Works, p.353 [emphasis added]
I am, I must confess, a great believer in the power of analogy.
Although an analogy is, in the end, only an analogy and must not be confused with the thing itself, it can be helpful.
As Steven Pinker notes above, the great thing about concrete analogies and models of abstract concepts is that they allow us to co-opt the inferential machinery of well-understood, concrete concepts and apply them to abstract phenomena: for example, we often treat time as if it were space (“We’re moving into spring”, “Christmas will soon be here”, and so on).
To that end, I propose introducing the energy stores and pathways of the IoP model to KS3 and GCSE students as tanks and taps.
Energy Stores = tanks
Energy Pathways = taps
Consider the winding up of an elastic band.
This could be introduced to students as follows:
One advantage I think this has over one of my previous efforts is that I am not inventing new objects with arbitrary properties; rather, I am using familiar objects in the hope of co-opting their inferential machinery.
Suggestions, comments and criticisms are always welcome.
My propositions are elucidatory in this way: he who understands me finally recognises them as senseless, when he has climbed out through them, on them, over them. (He must so to speak throw away the ladder, after he has climbed up on it.)
He must surmount these propositions; then he sees the world rightly.
— Ludwig Wittgenstein, Tractatus Logico-Philosophicus (1922), 6.54
[I]t is ambition enough to be employed as an under-labourer in clearing the ground a little, and removing some of the rubbish that lies in the way to knowledge;- which certainly had been very much more advanced in the world, if the endeavours of ingenious and industrious men had not been much cumbered with the learned but frivolous use of uncouth, affected, or unintelligible terms, introduced into the sciences
John Locke, An Essay Concerning Human Understanding (1690)
OK, so I was wrong.
In a previous blog, I suggested a possible “diagrammatic” way of teaching energy at GCSE which I thought was in line with the new IoP approach. Thanks to a number of frank (but always cordial!) discussions with a number of people — and after a fair bit of denial on my part — I have reluctantly reached the conclusion that I was barking up the wrong diagrammatic tree.
The problem, I think, is that unconsciously I was too caught up in the old ways of thinking about energy. I saw implementing the new IoP approach as being primarily about merely transferring (if you’ll pardon the pun) the vocabulary. “Kinetic store” instead of “kinetic energy”? Check. “Gravity store” instead of “gravitational potential energy”? Check. “Radiation-pathway-thingy” instead of “light energy”? Check.
Let’s look at the common example of a light bulb and I will try to explain.
Using the old school energy transfer paradigm, we might draw the following:
In spite of its comforting familiarity, however, there are problems with this: in what way does it advance our scientific understanding beyond the bare statement “electricity supplied to the bulb produces light and heat”. Does adding the word “energy” make it more scientific?
For example, when we are considering “light energy”, are we talking about the energy radiated as visible light or the total energy emitted as electromagnetic waves? It is unclear. When we are considering “heat energy” are we talking about the energy emitted as infrared rays or the increase in the internal energy of the bulb and its immediate surroundings? Again, it is unclear. In the end, explanations of this stripe are all-too-similar to that of Moliere’s doctors in The Imaginary Invalid, who explained that the sleep-inducing properties of opium were due to its “dormative virtues”; that is to say, sleep was induced by its sleep-inducing properties.
The problem with the energy transfer paradigm is that it draws a veil over the natural world, but it is a veil that obscures rather than simplifies.
The IoP, after much debate, collectively rolled up its sleeves and decided that it was time to take out the trash. In other words, they wanted to remove the encumbrance of terms that had, over time, essentially become unintelligible.
The new IoP model distinguishes between stores and pathways. For example, an object lifted above ground level is a gravity store because the energy is potentially available to do work. Pathways, on the other hand, are a means of transferring energy rather than storing energy. For example, the light emitted by a bulb is not available to do work in the same sense as the energy of a lifted weight. It is, within the limits of the room containing the bulb, a transient phenomenon. Many photons will be absorbed by the surfaces within the room; a small proportion of photons will escape through the window and embark on a journey to Proxima Centauri or beyond, perhaps.
Now let’s look at my well-meaning diagrammatic version of the energy transfers associated with a light bulb:
The stores are “leak-proof buckets” holding the “orange liquid” that represents energy. The pathways are “leaky containers” that enable energy to be transferred from one store to another. I have to admit, I was quite taken with the idea.
The first criticism that gave me pause for thought was the question: why mention the thermal store of the bulb? Surely that’s a transient phenomenon that does not add to our understanding of the situation. Switch off the electric current and how long would the thermal store be significant? Wouldn’t it be better to limit the discussion to two snapshots at the beginning (electrical pathway in) and end (radiative pathway out)?
The second question was: what does the orange liquid in the pathways represent? In my mind, I thought that the level might represent the rate of transfer of energy. Perhaps a high power transfer could be represented by a nearly full pathway, a low power transfer by a lower level.
But this led to what I thought was the most devastating criticism: why invent objects and assign clever (but essentially arbitrary) rules about the way they interact when you could be talking about real Physics instead?
Is there any extra information in the phrase “light energy” as opposed to simply the word “light”?
And that’s when I realised that I wasn’t helping to take out the trash; in fact, I was leaving the rubbish in place and merely spray painting it orange.
Now don’t get me wrong, I think there’s still a long road ahead of us before we become as comfortable with the IoP Energy newspeak as we were with the old paradigm. As a first step, I suggest all those interested should read and contribute to Alex Weatherall’s excellent Google doc summary to be found here. But I honestly believe that it’s a journey worth taking.
Opium facit dormire.
A quoi respondeo,
Quia est in eo
After a fascinating discussion led by the excellent Alex Weatherall (click here to participate in his Google doc Physics-fest — and follow @A_Weatherall on Twitter for more), I was thinking on possible teaching approaches for energy.
Although I think the IoP‘s (the UK’s Institute of Physics) approach is conceptually sound (see previous post here) and addresses many of the shortcomings in the traditional and time-hallowed “forms of energy” approach, many Physics teachers (myself included) are struggling to find direct and simple ways of communicating the highly nuanced content to students.
For example, to describe a filament bulb:
A (filament) light bulb is a device that takes energy in (input) through an electrical pathway (the current) to the thermal energy store of the filament (the metal is getting hotter) which transfers the energy through the radiation pathways of light (visible and IR). There is an increase in the thermal store of the room due to transfer via the heating pathway. The less energy transferred by heating compared to visible light the more efficient the light bulb.
I think this is in accordance with the letter and spirit of the “IoP Energy Newspeak” approach; but sadly, I can picture many students struggling to understand this, even though it was written by many hands (including mine) with the best of intentions.
But then I began to think of adopting a diagrammatic “enoji” approach. (See here for suggested energy icons, or energy + emoji = enoji)
Diagrams for Stores and Pathways
An energy store is represented by a “watertight” container. For example, the gravity store of a ball at the top of a slope could be represented thus:
Because it is an energy store, the amount of energy (represented by the level of orange liquid) in the store remains constant. Energy will not spontaneously leave the store.Energy stores don’t have holes. The unit we use with energy stores is the joule.
However, energy pathways do have holes. In contrast to an energy store, the energy level in a pathway will spontaneously decrease as the energy is shifted to another store.
To keep the energy level constant in a pathway, it needs to be constantly “topped up” by the energy from an energy store.
Since a pathway represents a “flow” of energy, the unit we use with an energy pathway is the watt (one joule per second). The “orange liquid level” in the pathway icon could therefore represent the amount of energy flowing through in one second (although I concede that this idea, though promising, needs more thought).
“Enoji Energy Shift” Diagrams
Adopting this convention, the “enoji energy shift” diagram for a ball rolling down a slope might look like this:
An energy store does not have any holes — unless it is linked to a pathway, like the gravity store above. Energy will move in the direction indicated by the energy pathway icon.
Simplified in a student exercise book, it could be represented like this:
The small upward and downward arrows are an attempt to indicate what happens to the energy level over time.
The Filament Lightbulb “Enoji Energy Shift” Diagram
This could be represented in a student exercise book like this:
Since there are no small up and down arrows on the pathway or thermal store enojis, this indicates that the energy levels are relatively stable (provided we have a constant input of energy from the power station). However, the energy level of the thermal store of the surroundings just keeps on going up…
Please note this is a work in progress.
I fully expect many teachers will think that the suggested set of conventions may well prove more confusing for students.
However, what I am attempting to do is to give students a set of simple, coherent yet serviceable analogies. In other words, this might provide a conceptual “tool kit” of physical representations of very abstract processes involving energy.
I hope readers will agree that it offers some scope for further development. Comments, criticisms and suggestions would be most welcome.
This has stayed with me from my PGCE course at Swansea University, many years ago. It was said by Frank Banks, the course tutor, in response to the question “What’s the simplest way to describe energy?”
And as pithy descriptions of energy go, it’s not half-bad. A small stone, dropped from the top of a skyscraper: lots of energy before it hits the ground — it could kill you. A grand piano, dropped from six feet above your head: lots of energy — it could kill you. Licking your fingers and touching the bare live and neutral wires in a socket: the conduction electrons in your body suddenly acquire a lot of energy — and yes, they could kill you. (With alternating current, of course, the electrons that will kill you are already inside your body — freaky!)
This attention-grabbing definition of energy seems to lead naturally to a more formal definition of “Energy is the capacity to do work“. This still leaves the problem of defining work, of course, but as R. A. Lafferty once said, that’s another and much more unpleasant story.
As I mentioned in an earlier post, I have been writing the Energy scheme of work for GCSE Science. As part of that brief, I wrote a short summary for my science colleagues of the IoP’s new approach to energy. I present it below without much amendment (or even a proper spellcheck) in the hope that someone, somewhere, at some time — may find it useful 🙂
The problem with teaching energy
One reason for the difficulty in deciding what to say about energy at school level is that the scientific idea of energy is very abstract. It is, for example, impossible to say in simple language what energy is, or means. Another problem is that the word ‘energy’ has entered everyday discourse, with a meaning that is related to, but very different from, the scientific one. [ . . .]
This ‘forms of energy’ approach has, however, been the subject of much debate. One criticism is that pupils just learn a set of labels, which adds little to their understanding. For example, one current textbook uses the example of a battery powered golf buggy. It asks pupils to think of this in the following terms:
Chemical energy in the battery is transformed into electrical energy which is carried by the wires to the motor. The motor then transforms this into kinetic energy as the buggy moves.
This, however, adds nothing to the following explanation, which does not use energy ideas:
The battery supplies an electric current which makes the motor turn. This then makes the buggy move.
A good general rule when explaining anything is that you should use the smallest number of ideas needed to provide an explanation, and not introduce any that are unnecessary
The new approach to the teaching of energy developed by the Institute of Physics (IoP) suggests that we limit our consideration of energy to situations where we might want to do calculations (at KS4, KS5 or beyond).
We should talk of energy being stored and shifted. The emphasis should be on the start and end of the process with minimal attention being given to any intermediate stages.
Consider the following examples:
lifting an object. Chemical potential energy store is emptied, and gravitational potential energy store is filled (note that we are not interested in intermediate motion as it doesn’t affect the final energy store).
rolling an object down a slope to the bottom. Gravitational potential energy store is emptied and thermal energy stores (of slope, of pen) increased.
Boiling water in kettle. Chemical store (from coal/gas power station) is emptied. Thermal store of water increased, thermal store of air increased, thermal store of kettle increased.
The new approach has been adopted by all UK exam boards for their new specs and is used in the AQA approved textbooks.
The following energy stores are considered: kinetic energy store, gravitational potential energy store, elastic potential energy store, thermal energy store, chemical potential energy store, nuclear energy store, vibrational energy store, electromagnetic energy store (note: the last is limited to situations involving static electric charges and static magnetic poles in magnetic fields).[NB Items in bold are those required for GCSE Combined Science.]
One major difference is that electric current and light are no longer considered as forms of energy. Rather, these are now regarded as means of transferring energy.
Neil Atkin recently wrote a fascinating post about the “New” approach for teaching the concept of energy to secondary school students, and provides some interesting commentary and some very useful links: go read!
I first came across the work of Ogborn and Boohan, on which much of the “New Approach” is based, in the 1990s. I remember embracing it enthusiastically. However, I subsequently returned to the more “traditional” kinetic-chemical-heat-potential-light-sound “naming of parts” model, mostly because many of the resources favoured by our students followed the older convention.
And so it has remained for a number of years, so I was all set to give the “New Approach” a proper rubbishing (as might be gleaned from my selection of the Gary Larson cartoon above) as a specious form of PC — physical correctness as opposed to political correctness, perhaps.
But as I read more about the “New Approach”, I gradually came to the conclusion that it is conceptually sound. More importantly, I think it follows one of the basic principles suggested by Engelmann and Carnine:
[I]f we are to understand how to communicate a particular bit of knowledge . . . we must understand the essential features of the particular concept that we are attempting to convey. Only if we understand what it is and how it differs from related concepts can we design a communication that effectively conveys the concept to the learner.
— The Theory Of Instruction, location 296
In other words, I think the “New Approach” is a more accurate representation of the physics of energy, and less likely to lead to misconceptions and false inferences.
Energy Is The New Orange
Read Dr Dav’s excellent blog post from 2013 for a clear summary of the arguments in favour of the New Approach, as well as Robin Millar’s excellent paper on the topic.
Rise of the Enoji
One of the suggestions made in the IOP’s Energy 11-14 is to use ideograms or icons to represent different energy stores.
By analogy with the ubiquitous ’emojis’ I suggest that we should call these energy icons Enojis. Who knows, it could just catch on…