e=mc2andallthat

The first rule of IoP Energy Club is: you do not talk about energy . . .

. . . unless you’re gonna do a calculation.

— with apologies to Brad Pitt and Chuck Palahniuk

In the UK, the IoP (Institute of Physics) has developed a model of energy stores and energy pathways that has been adopted by all the exam boards. Although answers couched in terms of the old “forms of energy” model currently get full credit, this will almost certainly change over time (gradually or otherwise).

This post is intended to be a “one stop” resource for busy teachers, with suggestions for further reading.

Please note that I have no expertise or authority on the new model beyond that of a working teacher who has spent a fair amount of time researching, thinking about and discussing the issues. What follows is essentially my own take, “supplemented by the accounts of their friends and the learning of the Wise” (if I may borrow from Frodo Baggins!).

Part the First: “Why? For the love of God, why!?!”

The old forms of energy model was familiar and popular with students and teachers. It is still used by many textbooks and online resources. However, researchers have suggested that there are significant problems with this approach:

1. Students just learn a set of labels which adds little to their understanding (see Millar 2014 p.6).
2. The “forms of energy” approach focuses attention in the wrong place: it highlights the label, rather than the physical process. There is no difference between chemical energy and kinetic energy except the label, just as there is no difference between water stored in a cylindrical tank and a rectangular tank. (See Boohan 2014 p.12)

The new IoP Stores and Pathways model attempts to address these issues by limiting discussions of energy to situations where we might want to do calculations.

Essentially, the IoP wanted to simplify “energy-talk” and make it a better approximation of the way that professional scientists (especially physicists) actually use energy-concepts. The trick is to get away from the old and nebulous “naming of parts” approach to a newer, more streamlined version that is fit for purpose.

Part the Second: How many energy stores?

The second rule of IoP Energy Club is: you do not talk about energy . . .
. . . unless you’re gonna do a calculation.

— with apologies to Brad Pitt and Chuck Palahniuk

The IoP suggests eight named energy stores (listed below with the ones likely to be needed early in the teaching sequence listed first).

Many will be surprised to see that electrical energy, light energy and sound energy are not on this list: more on that later.

There are, I think, two very important points:

1. All of these energy stores represent quantities that are routinely measured in joules.
2. All of the energy stores represent a system where energy can be stored for an appreciable period of time.

For example, a rattling washing machine is not a good example of a vibration energy store as it does not persist over an extended period of time: as soon as the motor stops, the machine stops rattling. On the other hand, a struck tuning fork, a plucked guitar string or a bell hit with a hammer are good examples of vibration energy stores.

Similarly, a hot object is not a vibration energy store: it is better described as a thermal energy store. Thermal energy stores are useful when there is a change in temperature or a change in state.

Likewise, a lit up filament bulb is not a good example of a thermal energy store because it does not persist over an extended period of time; switch off the current, and the bulb filament would rapidly cool.

Note also that the electric-magnetic energy store applies to situations involving magnets and static electric charges. It is not equivalent to the old “electrical energy”.

The thread linking all the above examples is we limit discussions of energy to situations where we could perform calculations.

Thermal energy store is an appropriate concept for (say) the water in a kettle because we can calculate the change in the thermal energy store of the water and the result is useful in a wide range of situations. However the same is not true of a hot bulb filament as the change in the thermal energy store of the filament is not a useful quantity to calculate (at least in most circumstances). For further discussion, see this blog post and also this section of the IoP Supporting Physics website.

Part the third: How many energy pathways?

The third rule of IoP Energy Club is: there ain’t no such thing as ‘light energy’ (or ‘sound energy’ or ‘electrical energy’).

— with apologies to Brad Pitt and Chuck Palahniuk

In the new IoP Energy model, there is no such thing as a “light energy store”. Instead, we talk about energy pathways.

Energy pathways describe dynamic quantities that are routinely measured in watts. That is to say, they are dynamic or temporal in the sense that their measurement depends on time (watts = joules per second); energy stores are static or atemporal over a given period of time.

It is not useful to talk about a “light energy store” because it does not persist over time: the visible light emitted by (say) a street lamp is not static — it is not helpful to think of it as a static “box of joules”. Instead it is a dynamic “flow” of joules which means its most convenient unit of measurement is the watt.

As an analogy, think of an energy store as a container or tank; in contrast, think of a pathway as a channel or tap that allows energy to move from one store to another. )

You can read more on the “tanks and taps” analogy here.

The cautious reader should note that the IoP describe slightly different pathways which you can read about here. (Mechanical and Electrical Working are in, but the IoP talk about “Heating by particles” and “Heating by radiation”; on this categorisation, sound would fit into the “Mechanical Working” category!)

The fourth rule of IoP Energy Club is: I don’t care what you call it, if it’s measured in watts, it’s a pathway not an energy store, OK?

— with apologies to Brad Pitt and Chuck Palahniuk

You can look forward to more ‘IoP Energy Club Rules’, as and when I make them up.

Important note: all of the above content is the personal opinion of a private individual. It has not been approved or endorsed by the IoP.

References

Boohan, R. (2014). Making Sense of Energy. School Science Review, 96(354), 33-43.

Millar, R. (2014). Teaching about energy: from everyday to scientific understandings. School Science Review, 96(354), 45-50.