We talk about energy all of the time. We all have an idea of what energy is, sometimes several conflicting ideas.
Everyday ideas of energy: Red Bull gives you wings.
Underlying all of our ideas of energy lies the idea that energy is a substance which you can use up. Probably most of us don’t move beyond this idea.
From a science perspective, this isn’t correct – energy isn’t a magical substance which can be used up or generated – but this is the language that surrounds us. Even science teachers and popular science presenters use the word in this sense.
Is that a problem? Well, yes. It can lead to common misconceptions:
human activity – I’m tired because I have run out of energy or I can run very fast because I have a lot of energyhttps://www.stem.org.uk/sites/default/files/pages/downloads/BEST_Article_Teaching%20energy.pdf
health – as in ‘exercise is good for you because it builds up your energy’ and ‘when we run out of energy we need medicine and vitamins’
food and fuels – some objects and materials contain a lot of energy that can be used up to help us move about and to make other things happen.
How We Used to Teach Energy
When I learnt about energy, we used to talk about ‘types’ of energy and energy ‘transformations’ from one type to another. This layer of language and understanding sits on top of the everyday usage without too much difficulty. It isn’t philosophically different – energy is still seen as a substance which can move about and change from one type (e.g. kinetic) to another. I suspect I haven’t moved beyond this model.
Is this model a problem? Well, it is better than the everyday concept, but it still leads to problems. There aren’t really many types of energy and you can’t really say where the energy is. The model is fundamentally incorrect, but you can (mostly) solve problems with it.
How We Teach Energy Now
The modern way of teaching energy is an improvement on the ‘energy types and transforms’ model. Energy is still conceived as a sort of substance, but there is only one ‘type’ of substance. This substance can ‘shift’ from one ‘energy store’ to another. So a car might have a kinetic store and a chemical store. The energy shifts from the chemical store to the kinetic store (see here).
When we try to think about energy moving, we come to a conceptual difficulty: is there a light store of an electricity store? It is more convenient, and less prone to cause a misconception, simply to think about the start store and the end store.
In addition, we try not to suggest that energy causes anything, rephrasing sentences which suggest causation (e.g. change: ‘marathon runners consume energy bars to run further’ to ‘marathon runners consume carbohydrate bars to run further’).
Is this model a problem? Well, it is better than the previous two models used because the types of energy is replaced with the idea that there is only one type of energy – but that this energy exists in different ‘stores’.
What Energy Really Is
The most accurate concept of energy is to admit that we don’t really have an understanding of what energy is. We don’t think there are different ‘types’. It doesn’t flow. It isn’t really in a specific place.
All we really know if that for a system, there is a quantity that doesn’t get created and doesn’t get destroyed. It is an accounting concept. We can calculate with it, but we have no business really trying to picture what it is or saying that it causes anything.
The best I can do with this is to think of energy like money in global markets. The money doesn’t really exist anywhere. It doesn’t do anything, but you can calculate it. It’s not a perfect simile, but it’s the closest I’ve been able to get.
Most of us get through life with incorrect mental models of what energy really is (me included). These models lead to us misunderstanding how the universe really works. That’s a shame, but there are bigger problems facing us.
The ‘energy stores’ model is a decent compromise. It would be interesting to see whether the stores model really does generate fewer misconceptions that the ‘energy types’ model. I suspect it does. It is unlikely that the ‘stores model’ causes issues for further study. It may be confusing for pupils when they hear a blend of the stores and types model used in the media and in lessons – though I doubt it causes real problems. In short, try not to let it knock your confidence.