There are many different methods used to conceptualise energy.
One uses a liquid moving between containers, but I have a couple of problems with it. What are the containers? If the container is filling up then it has a size. What does the container size represent? Different energy forms are represented as being in different containers with different labels. ?
As you are probably aware, I like to keep metaphors simple, based on concrete metaphors and easily visualised.
So here's mine:
There are just 4 concepts to get over.
- Energy is just energy (measured in joules) whatever its form.
- Energy cannot be lost or created - conservation of energy.
- When something is happening energy is changing 'form'/for something to happen energy must change 'form'
- Energy never ends up in just one form - entropy
Visualise energy as a mystical malleable substance (plasticine or play dough are familiar substances to use as a starting point).
The 'mystical plasticine' has a definite 'amount' which you measure in joules. A piece twice as big is double the joules.
You have what you have. As a child playing with real plasticine you are aware of that. None magically appears and neither does it evaporate.
We can however add bits from elsewhere and takes bits away and put them elsewhere.
Energy can be in a certain number of shapes (depending on how many 'forms' of energy the students have been taught). As form can be used in the context of shape this is straightforward.
When something happens the energy changes shape/form. When energy changes shape/form something happens.
We get over the idea that energy changing form = something happening.
E.g. when something falls energy in 'gravitational potential energy shape' changes into 'kinetic energy shape'
Whenever energy changes shape/form a piece breaks off.
This conceptualisation metaphor is based on a familiar concrete concept. In this case plasticine. It is a mid-point from concrete to abstract, if you like. You can't stretch the metaphor too far - all models break if you treat them too roughly. What it does do is lay the foundations and put the scaffolding up to help develop an understanding of such an abstract idea as energy. There are no superfluous additions in the model. There is just energy and its form.
Once this metaphor has been assimilated, the 4 fundamental concepts are now there. Further abstraction in future will be easier as the pupils are halfway there already.