The more abstract a concept is, the less useful learners find definitions or explanations. There is no lightbulb moment. Rather, our understanding grows by a gradual accumulation of experience, of problems solved.
Energy is a perfect example of this:
“It is important to realize that in physics today, we have no knowledge of what energy “is.” We do not have a picture that energy comes in little blobs of a definite amount. It is not that way. It is an abstract thing in that it does not tell us the mechanism or the reason for the various formulas.“
Richard Feynman, in The Feynman Lectures on Physics (1964) Vol I, 4-1
We do not know energy what energy “is.” We cannot model it or visualise it. The equations highlight this: energy must always be calculated from more accessible quantities. We use mass and velocity for kinetic energy; mass and height for gravitational potential energy; the spring constant and the displacement for elastic energy; the mass and change in temperature for heat energy and the change in mass and the speed of light for nuclear energy.
Feynman explains that energy:
“is not a description of a mechanism, or anything concrete; it is just a strange fact that we can calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same.”
Feynman, 1963, p. 4-1
So, there is no point trying to explain what energy is. Just give lots of examples. Thomas Kuhn, the 20th century philosopher of science, got it right: we learn through an accumulation of examples (here). This is important for teachers. Give an explanation, share definitions, read the texts and the stories. But the real route to understanding energy is by doing, and learning, all of the problems at the back of the textbooks, the exam questions (old and new) and the standard practicals.
The problems reveal something else for teachers: for generations, we have taught energy wrong. Or at least unhelpfully. You can hear it in the speech of experienced physicists: we talk about types of energy as though they were all the same sort of thing, as though kinetic energy were in principle the same sort of thing as electricity and sound.
But our calculations show us something different.
Of all of the “types of energy” we talk about in school, we only calculate kinetic energy; gravitational potential energy; elastic energy; heat energy; chemical energy and nuclear energy. We use these a lot. But we don’t calculate sound energy or light energy. And we don’t really think about electrical energy unless we talk about the flow of electrical energy – and then we are really talking about power.
There is something distinctly different about these two groups of energy.
In the UK, the Institute of Physics have taken this idea and proposed a way of teaching energy. Kinetic energy, the potential energies, heat, chemical and nuclear energies are all described as ‘energy stores,’ whereas electricity, sound and light are more helpfully described as ‘energy pathways.’
Then the Institute of Physics recommends that we change the way we teach energy transforms: don’t show the intermediate stages – just the beginning of the process and the end. It has always been unconvincing to try to show all of the intermediate stages in any case: you end up with confusion. Keep it simple.
This avoids messy and unhelpful thinking in young physicists. They are not learning something that they then have to unlearn later. The accumulation of exemplars can carry on, without the burden of exemplars which hinder.
Further reading and resources:
- Robin Millar’s excellent paper: Teaching About Energy.
- Ian Horsewell’s series of blogs on the language of energy is very helpful, part 1, part 2, part 3 and part 4.
- E=mc2andallthat’s blog on getting it a little bit wrong is also very insightful: IoP Energy: It’s About The Physics, Stupid!
- The Institute of Physics’ energy teaching resources.