Bringing together two sets of constraints

Focusing on the learners:

Distinguishing–eliciting–connecting. How to:

• distinguish between the physical descriptions of the lived-in world and the descriptions using the idea of energy
• avoid being drawn into conversations where energy is the ultimate cause
• build a semi-quantitative model of energy that pupils can reason with

Teacher Tip: These are all related to findings about children's ideas from research. The teaching activities will provide some suggestions. So will colleagues, near and far.

Focusing on the physics:

Representing–noticing–recording. How to:

• represent conservation and dissipation
• use mechanisms to explain why things happen: energy calculations to explore what can happen

Teacher Tip: Connecting what is experienced with what is written and drawn is essential to making sense of the connections between the theoretical world of physics and the lived-in world of the children. Don't forget to exemplify this action.

Taking an energy approach

Thinking about the learning

Although the concept of energy is one of the most important ideas in science, it is not helpful to try to explain every situation and process in terms of energy. There are some occasions for which energy explanations are helpful and some for which they are not. An important part of learning about energy is coming to recognise when it is appropriate to use energy ideas. Taking an energy approach is helpful when thinking about:

• How much? problems. For example: How high will the rubber ball rebound to when dropped?
• Whether or not a process will happen. For example: Will the electric battery keep the bulb lit for longer than one hour?

Thinking about energy is not a useful route to go down when you want to know why something happens. For example: Why does the rubber ball rebound when dropped to the ground?

Energy approaches tell us nothing about physical mechanisms. Explore these examples to help you understand when and when not to use energy ideas.

Energy is not the cause

Wrong Track: The pram speeds up because its energy increases.

Right Lines: The parent pushes on the pram making it speed up, or accelerate. As a result energy is shifted to the kinetic store of the pram, but it is the force that actually makes the pram speed up.

Using other ideas

Thinking about the teaching

You might come across statements such as these:

• Without energy nothing can ever happen.
• You need energy to move and to do jobs.
• Energy is needed to get jobs done, or to make things work.
• A bike keeps moving because it has energy in its kinetic store.

Such statements cast energy as the cause of processes and reflect an everyday way of thinking about energy. However, from a scientific point of view, this is not correct. Energy does not make things happen. You can be sure of this because energy is conserved: the energy before a process is the same as energy afterwards. If the amount of energy does not change how can it make anything happen?

So try to avoid statements like those above in your own teaching. It is better to use other ideas (such as force) to explain why things happen. Using energy can sometimes explain why some processes cannot happen, and give other insights, but it cannot be rightly considered a cause.

Energy stores as rubber bands

Any energy store must be in some way like a stretched rubber band, since the band itself is a store. Filling energy stores is just like stretching rubber bands: emptying them is just like allowing rubber bands to relax again. Relaxing the rubber band allows some other job to be done – perhaps something gets lifted, or the band itself gets warmed.

Teacher: See how the stores that we have already introduced are like the rubber band.

Teacher Tip: When teaching about energy it is always helpful to have a few rubber bands to hand to make connections with different kinds of energy stores. For example, lifting a book up and increasing the amount of energy in its gravitational store can be likened to stretching the rubber band. Just as the stretched rubber band has a store of energy, so does the book in its elevated position in the Earth's gravitational field.

There's a good chance you could improve your teaching if you were to:

Try these

• developing an energy calculation only where the calculations would be insightful
• developing the idea that calculating the energies constrains what is possible

Teacher Tip: Work through the Physics Narrative to find these lines of thinking worked out and then look in the Teaching Approaches for some examples of activities.

Avoid these

• dragging energy into the description of every process
• using energy as a part of a mechanism in a causal explanation

Teacher Tip: These difficulties are distilled from: the research findings; the practice of well-connected teachers with expertise; issues intrinsic to representing the physics well.