Energy Stores and Pathways

Tonight’s #asechat will involve Charles Tracy, the IoP’s Head of Education (and one of my bosses), discussing the new approach adopted by exam boards from this year. There’s lots of information at Supporting Physics Teaching, which is free to access and needs no sign-in. Other sites and resources will hopefully move over to this terminology (BBC Bitesize already has, for example). But why should we bother?

Energy is one of those topics, isn’t it? We teach it several times, but the kids seem to hang on to their misconceptions. Partly this is because it’s a word which is used in everyday life, often interchangably with power. Partly it’s the way students get mixed up with energy ‘resources’ (or as I prefer to teach it, ‘ways to make electricity’.

We shouldn’t be surprised that this causes problems. Energy is at heart a very abstract concept, and so one which is difficult for students to grasp. Does it make things happen? Well, not always – and this leads to students confusing energy with force. I used to divide the ‘types’ of energy into potential and moving categories, which I suppose could be seen as a crude version of this new approach.

In the simplest possible description, energy is about bookkeeping or currency. It turns out that when objects interact, often via forces, then we can do some maths which describe the change. What’s interesting is that if we pay attention, then the same number comes up more than once. This tells us that something is conserved.

We call that something energy and say it has been transferred from one place to another. Calling those places stores emphasizes that they still have whatever they were given. This sounds similar to past approaches but avoids the idea of distinct ‘chemical energy’ being turned into ‘electrical energy’ and so on. SPT has a good comparison.

So we teach energy concepts to make it easier to do calculations. We can’t measure energy directly, but the equations we use allow us to make measurements, which allow us to make deductions, which in turn allow us to make predictions.

That sounds a lot like science, doesn’t it?

Energy moves from one store to another via pathways. These are actions – verbs, if you like – which describe a change in a system. The IoP is suggesting using the word shift rather than transfer. (I would suggest one good reason to do so is to avoid the mix up with transform, which suggests there are different kinds of energy.) I found the diagram of possible pathways at SPT useful.

Several approaches are possible, including taking a ‘snapshot’ before and after an event, or showing the amount of energy in each store with orange liquid. There are of course others, many of which are visual and so provide an anchor for students to observed reality. This isn’t to recommend VAK of course – only to suggest that making this concept ‘stract’ can only be a good thing.

I’ll be taking part in the session this evening, and I’ll add a link to the archive afterwards. I’m sure there’ll be an advert for TalkPhysics, which is one place to get access to ongoing advice and support on this and other approaches. It may be short notice but please pass on the link for tonight’s chat; the more the merrier.

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