## Preparing the ground for thinking with energy

### Tilth

Well, we now have an image of a description; how can we prepare the ground?

1. Foregrounding constraint relationships – those which show possibilities and impossibilities – for changes where the quantities are less abstract. (Showing what is necessary for a sound level two description).

2. Developing the idea of a trade-off, thus establishing that there may be choices in getting a job done, but there are hard limits to those choices. (A gentle introduction to conservation laws: not getting something for nothing.)

3. Developing a semi-quantitative description for the calculated stored quantity that is energy (and maybe also a linked version for power). (Laying up resources for developing a level three description for students whose algebraic and arithmetic competence is limited)

(This last one is reasonably well-rehearsed and tested, mainly through the influence of the Supporting Physics Teaching initiative. )

### Representing energy

A tangible representation for a quantity of energy can support reasoning about how much ends up enabling different processes.

A calculated quantity of energy can be thought of as a volume of orange fluid. This builds on both the materialist and substantialist approaches to the teaching of energy.

Wrong Track: Energy is a fluid-like substance (caloric rebooted!)

Right Lines: Quantities of energy can be thought about metaphorically as volumes of orange fluid, which are shifted from store to store without getting lost. To find out how much is shifted, do a calculation. The calculation depends on the store, which is just a placeholder for the calculation.

You could use blocks, like Feynman, but orange fluid has better affordances (it's not quantised, for a start!).

### Energy as an orange fluid

Purists suggest that you should think of energy only in abstract mathematical terms, but for some this is not helpful. You can think of energy as an orange fluid which is contained in stores. I think that not much harm will come from this in elementary studies, and it may help to make energy more intelligible because there is something to manipulate.

There are mappings to exploit:

volume of orange fluid → quantity of energy
fluid can be moved around → energy shifted;
can't just disappear → energy conserved;
fluid can be spread out to many locations → energy is dissipated.

You can model all of these physically with orange fluid.