Energy Language Thoughts Part 4

Parts 1 (Introduction), 2 (Pathways/Processes) and 3 (Stores) are all available and will help make this more useful. Please continue to comment, on whichever post seems most relevant, if you’ve any queries or suggestions. Thanks to those who have already done so.

Practical Approaches

The IOP guidance begins by taking snapshots before and after an event and describing the changes to various possible associated stores. The alternative is to think about the physical processes – which will be variably familiar to students, depending on age – and thinking about the effect they have on parts of the system. YMMV.

The famous energy circus can be used, but be cautious! Some make much clearer examples than others. In most cases you will need to be very specific about the start and end points you wish the students to consider. I recommend checking out the SPT guidance. In particular, the ‘one step at a time’ diagram shows why chains of energy can cause problems. The suggestion there, which I endorse, is that you:

1. start with the idea of fuels ie chemical stores
2. make clear that fuels limit effects, they don’t by themselves cause the effects
3. give high, hot and stretched objects as equivalents, but as they’re clearly not fuels we associate them with
4. gravitational, thermal and elastic stores respectively

Explained at SPT

I’d suggest looking at your energy circus for clear demonstrations of these to begin with. Next would come a kinetic store, probably as an endpoint. A gyroscope or Newton’s cradle is a nice example of a kinetic store which lasts long enough to be plausible.

Approaches to consider

You could have a first round to develop some basic ideas, then a second with more complex snapshots (either more than one store involved at the end, or the same kind of store but associated with different objects).

Have students identify just the stores to begin with, discuss them as a class, then come back and add descriptions for the processes. This could be split between lessons; that way you can provide correct stores in the second lesson and concentrate on processes. In some cases, such as the classic filament bulb, two similar pathways will be needed.

• From: thermal store of filament
• Via: heating by visible radiation, heating by IR radiation
• To: thermal store of air in the room

If you want them, here are energy-circus-cards as pdf (includes example and blank cards)

Provide sets of laminated cards with stores, and arrows for the descriptions of processes. Labelled arrows are of course an option, but be aware of limitations and I’d include some blanks.

Again, cards-for-energy-v3 as pdf to save you a few minutes.

An extension could be to suggest measuring equipment and/or units for the relevant stores in each situation. If returning to these examples at GCSE, then recall of the equations are the natural next step.

Consider including actual photographs for some situations that cannot be easily reproduced in the lab; this would be a good way to introduce some examples from biology and chemistry. A food chain in biology might, for example, be described so:

• From: chemical store of lettuce
• To: chemical store of rabbit

Then

• From: chemical store of rabbit
• To: thermal store of rabbit, kinetic store of rabbit, chemical store of fox

And finally

• From: thermal store of rabbit, kinetic store of rabbit
• To: thermal store of air

For chemistry, exothermic reactions will involve heating by particles and/or heating by radiation pathways. If the material explodes (which in my experience is the preferred result) then there is some kind of mechanical working too, yes? Be prepared for questions about state changes; the best approach is that latent heat means the thermal store is not only identified by the temperature change. Which, yes, is a complication.

It’s probably worth adding notes – mental or otherwise – to the other science topics so you can remind students of the new language. If you have particular queries, drop me a line in the comments or, for a more considered answer, join in with the discussions on TalkPhysics.

This seems like a good chance to consider the Big Ideas in Science Education. Which should be up anyway, somewhere, but it’s always nice to have a reminder.

Exams and Textbooks

This is where I must admit defeat. I know – in fact I started the first post in this series with this point – that teachers want to know what will get marks and what won’t when it comes to the exams. Sadly, I don’t know. At least one board used the old language in the sample papers originally made available. The list of stores is not consistent between boards, though I hope that makes more sense after Part 3. And so on.

I’m sure we’ll all be happier once we see more examples of possible questions, but I’m not involved much with the boards so I have no insight. My advice – which isn’t official IOP guidance, nor is it specially informed – is that if your students can explain the mechanisms behind the transfers, they shouldn’t need to worry about the language, either pathways or processes. For the stores, it’s probably more important that they can identify the equations that are relevant and be able to do the maths – that, of course, hasn’t changed! I’ve recently discovered that Richard Boohan is putting together some materials; I shall be watching with interest.

Whether students will be penalised for talking about light energy, sound energy, electrical energy – that I don’t know. I also don’t know how much emphasis will be placed on this language by those marking biology and chemistry questions. So I’m not much good, really. Sorry!

Last appeal for comments, feedback, criticism… please let me know what you think of these four pieces. At well over 3000 words I appear to have accidentally written an essay. I hope that if you’ve waded through it, you feel it was worth your time. Please do give me a shout if there’s something I can do to improve the time spent vs time saved ratio.

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Energy Language Thoughts Part 3

As you would expect, this follows on from Part 1 (Introduction and Summary) and Part 2 (Pathways/Processes). Even if you’ve read them, you might want to look back at the comments readers have made  – many thanks to everyone who has been able to take the time.

Descriptions vs Labels: Stores

The stores are not simply renamed ‘energy types’. A lot of them use similar words, but that’s because they’re trying to describe the same physics. They represent the changing properties of a part of the system, caused by it gaining or losing energy. When a steel block undergoes physical processes, it changes in a measurable way. It might change shape. Its temperature might change. It might be moved away from the Earth’s surface. It is a shame that exam boards are taking different approaches, but the eight suggested by the IOP are:

• chemical store
• thermal store
• kinetic store
• gravitational store
• elastic store
• nuclear store
• vibration store
• electric-magnetic store

More details at SPT

Like the processes, there are sometimes more than one way to consider what is happening. If a gas is heated, the change could be considered in terms of the measured temperature change (thermal store), or in the increased movement of the particles (kinetic store). Realistically, there are not many situations where two stores will seem equally appropriate. And when they are, this is actually a strength. The two approaches will give values for the energy change which are the same. Energy is energy, whether it is considered in the context of a thermal or kinetic store. The whole point of using energy as a ‘common currency’ is that is translates between contexts.

The stores, as discussed in my introductory post, are each a way of considering a physical measurement and an associated equation. The idea is that you consider the ‘before’ and after’ situations for relevant stores, as snapshots. (The exception, for school-age students at least, is a chemical store where the values are found empirically.) I produced, based on some ideas from IOP colleagues, some energy store ‘bookmarks’ which bring together the different aspects. They wouldn’t take long to put together, but you’re welcome to my version:

stores-bookmarks as pdf

Common Variations

The vibration store can be considered as a kinetic store which oscillates. The easier measurement is not speed but amplitude and time period. Imagine trying to find a meaningful value of the speed of a swinging pendulum, for example. But some boards are omitting it, which is fairly easy to justify.

I’m less happy that at least one exam board (AQA) miss out the nuclear store entirely. This seems like a huge mistake to me as it uses the one equation pretty much everyone knows from physics, E = mc2! It would also make it impossible to start with the sun, which makes most biology a bit tricky. (From nuclear store via particle heating processes to sun’s thermal store then via radiating processes to Earth’s thermal store and biomass chemical store)

The electric-magnetic store – not electromagnetic – is about the position of objects within two kinds of field. Now, I know they’re related – Maxwell’s equations and all that – but I think for most students it’s a lot easier to consider two separate stores, the magnetic and the electrostatic. The upside is that this means you can clearly link them to gravitational stores and so cover fields as a ‘meta-model’. The downside is that it makes the stores list look even more similar to the old approach. If you take this tack, make sure you emphasize that it’s an electrostatic store to clearly distinguish from the electric current pathway.

Which brings me to…

What about light/sound/electricity?

The SPT resources have some very good explanations on this. My reasoning is that they are processes which only have meaning if we think about duration. To describe them in numbers, we use power in Watts rather than energy in Joules. So they are, obviously, real physics effects. But they fit best into this model as processes shifting energy between stores, rather than stores themselves.

Disclosure: my issue with this is that a very strict interpreation of thi would seem to rule out kinetic stores as well. The snapshot approach – comparing the change to stores in between two static frames – makes it hard to reconcile a moving object with a single instant. Hmm. Although we have no problem with considering momentum at a moment in time, yes? Contrariwise, students may have an image of light as being made up of photons as moving objects, or when older the equation E=hf. Hmm again. And what about latent heat? This is best considered as a special term of the thermal store, but it’s not obvious. (Thanks to my colleague Lawrence Cattermole for reminding me of this today.) Of course, no model is perfect. The test is whether this approach is better than the ‘types’ of energy approach that has been so pervasive.

‘Better’, of course, is not a very scientific term! It is more accurate when describing the physical processes. The words are a closer narrative match to the equations students will need to use as they develop their physics. The model is different to what we and our students are used to, but objecting to it on that basis seems short-sighted. As I originally said, you could argue that the timing is unfortunate, with new specs and grading systems, but I don’t think we’d ever be at the point where all science teachers welcomed a change with open arms.

As always – please comment, respond, shout angrily at me using the field below.

Energy Language Thoughts Part 2

The previous post was a summary or introduction – thanks to all those who have commented already – and tomorrow I’ll be moving on to stores in more detail. But for now…

Descriptions vs Labels: Processes

To make life easier, humans like to use shorthand for complex processes. These are categories or labels, not detailed descriptions. Many pathways or processes can be put into one of these categories, but the aim should always be end up able to describe what is actually happening.

• Heating by particles
• Radiating (aka heating by radiation)
• Electrical working
• Mechanical working

Longer explanation at SPT

How we choose these categories will alter our interpretation. For example, are sound waves a form of mechanical working? Or do we include all waves in the ‘radiating’ category? The physics description of what is happening is what we and our students should be concentrating on, because it doesn’t change. The ideas about Johnstone’s Triangle that I’ve read about via Michael Seery’s blog, from chemistry education, has obvious parallels.

Reproduced from Michael’s post, credited to University of Iowa.

If we can link the macro (observations in lab) and sub-micro (particles and interactions) levels, the symbolic can wait. A similar discussion is had on SPT about alternating between the lived in world and a theoretical model.

Avoiding using these categories – which by their very nature are imprecise – might be worth considering. It would be very easy for students to think they have to assign any physics process to one of the four listed above, without really thinking through what’s happening. (If you’d like to consider symbolic approaches, I’d suggest checking out the physical versions of energy bar charts as described here by Greg Jacobs.)

As pointed out by several – most recently Richard Needham on Twitter – changing how energy is described in physics lessons means nothing if we can’t apply this to biology and chemistry. And it needs to make more sense there too! In school chemistry, heating and radiating (in the form of light-emitting) will be the significant processes. The equations used later on for enthalpy change – endo and exo-thermic reactions and so on – work nicely with this framework. In school biology, the transfer of energy is usually about photosynthesis (a radiating pathway fills a chemical store by the production of glucose/oxygen) or nutrition/metabolism. (More about stores in the next ‘chapter’.) One of my jobs is to have a closer look at the KS3 specification for any mention of energy in chemistry and biology and see what I’ve missed – please let me know in the comments if this has been done already!

I’ve heard – and contributed to – discussions about other possible pathways, perhaps useful for younger students. The regular suggestion is reacting, which would include chemical reactions in cells (aka metabolic-ing) as well as the lab. The shift happens between two chemical stores. The physics process, if we look closely enough, is about electron exchange between atoms. But I wouldn’t want to have that level of explanation in a year 7 lesson! As ever, the question is about us choosing a realistic level of detail for our students at any particular time.

The Power of Processes

I wrote earlier that we weren’t interested in how quickly a process worked. That’s obviously not always true; rates are very important in physics! So the process can happen quickly or slowly, which changes the magnitude of the final change in the relevant stores. This tells us that processes are about power, not just energy. (Thanks to Brendan Ickringill who pointed out the word rate is important.) The analogy I use is that of the carbon cycle. Asking how much carbon is ‘in’ plant biomass at any point is a meaningful question, if not an easy one. But it makes no sense to ask how much carbon is ‘in’ combustion, or any other process. They are rates, not amounts.

My colleague Trevor Plant reminded me of the need to change how we use Sankey diagrams for this new approach. The width of the arrow can now describe the power of the process, transferring or shifting energy between stores. A lot of the same questions could be asked, and efficiency is still a helpful consideration. We’d now think about useful processes (with values in watts) and wasteful or dissipative ones. As ever, we’d need to distinguish between similar processes; for example, energy shifted to the thermal store of water in a kettle is useful, whereas heating of the air around it is not.

Effectively what we’re doing here is describing what the ‘magical arrow of energy transfer’ is symbolising. A useful resource is a set of laminated arrows which students can write on for descriptions of the physical processes. You could provide some with descriptions on them, but the danger is that the class – or the loudest member of it – will then choose a best-fit rather than something more accurate. If you also supply laminated cards – as boxes, not arrows – with the eight stores on them, they are ‘encouraged’ towards the new model. These might be particularly useful to analyse a chosen selection from the famous energy circus.

On this theme, I produced some cards to go on the electrical sockets in the lab. The idea is to remind students that the current comes from somewhere else, and that the electrical supply is a pathway/process, not a store. Download below.

power-stations as pdf

As before, I hope the discussion here is useful – and please respond in comments if there’s something I’m missing out! Next post will be looking at stores in more detail, then hopefully a last one at the weekend on practical approaches and ways to adapt what you used to use!

 

Energy Language Thoughts Part 1

I was thinking ‘out loud’ on Twitter about the ‘new’ energy language, discussions prompted in part by science teachers applying the changes in their classrooms. I know I’ve blogged about energy before, but thought it might be time to have another crack at it. I’m not writing here in an official IOP capacity, although I’m also swapping these ideas with colleagues. All thoughts, responses, criticisms and offers of coffee accepted. And if you add the comments here it will be easier for others to join in, as twitter replies get lost after a while. Alternatively, as the responses to a twitter poll led me to post it in chunks, you might want to wait until it’s all done. I’ll crosspost the complete thing to TalkPhysics as well.

Challenges

• Resistance to change – teachers as much as students!
• Students who have learned one approach in KS3 and are now being told something different for KS4.
• The exam boards can’t seem to agree on which stores to use and which to omit, which has knock-on effects for textbooks.
• Teachers don’t know which answers will get marks in the exams, so don’t know what advice to give students.
• Existing resources are incompatible with the new language – but with enough similarities to make it look like they’ll work (like a false friend in language teaching, which gives you confidence while misleading).

I don’t have answers for these. To be honest, nobody does! What I can say is that many people are trying to figure out the best way to make these changes work well for everyone. It is, in my personal view, unfortunate that they are coming in with both a specification and a grading system that are new. It’s worth noting the stores and pathways model hasn’t been recently  invented by the IOP to annoy teachers. For example: Robin Millar, Practical Physics.

There’s lots on the Supporting Physics Teaching resource from the IOP, but one place to start is this suggestion about useful things to keep in mind.

Hopefully Helpful Thoughts

A good thing about the ‘new’ language is that it encourages – pretty much demands – more attention on the actual physics. That’s the point. What is happening? So let’s start there; in any example, what process is involved? Some materials/sources call these pathways, but the idea is the same. Let’s not get hung up on labels for them, but on descriptions of actual events. It may help to emphasize to yourself that they are verbs, not nouns. They can happen fast or slow. But they involve actual physics, forces and EM and heating and so on (obligatory link to the Big Ideas of Science Education, because it’s awesome. When I rule the world every school science lab will have a huge poster of these.)

Now, these processes will change something. It means we can measure something which is different after this process compared to before. We’re not interested, right now, in how quickly this change has occurred – just that it has. This is a change – maybe a temperature increase, a greater separation of two objects, whatever – in a measurable quantity. This is associated with what we call a store. Different kinds of store have different equations, which link the measurable quantities together along with some constants. The result of that equation is a value for the energy associated with that store.

If we pay closer attention, we find that (at least) two stores have changed. What’s really interesting is that if we’re really careful, when we compare the equations, we find that the numbers are the same. An increase in one store is always balanced by a decrease in the other. The equations work as an exchange rate, showing how temperature rise in one part of the system is ‘worth’ faster movement in another part.

This, of course, is the principle of conservation of energy. Energy isn’t lost. But we can lose track of it. Sooner or later, the processes end up heating up the entire universe. Because the universe is pretty big (no, bigger than that) the change in temperature is effectively immeasurable.

So there we are; a very brief introduction to the ‘new’ model. More posts coming up, hopefully one per day. The sooner you comment, the more likely I can address your suggestions in the course of the series!