This is a summary of our special Physics Education presentation at the Annual Meeting of the Association for Science Education held at the University of Birmingham, January 1997.

It was most encouraging to find an audience of 24 gathered at 9am on a bitter January morning to receive our presentation, particularly since the competition included such gems as 'Is our science curriculum full of holes' and 'do bacteria have sex?'. The audience was a mixed bag of people from all phases including teacher education.

Our aim was to trace the development of force and motion ideas as they appear in the National Curriculum at Key Stages 1 to 4 and then look at what A-level exams expect of students post-16. Interwoven within this development we placed a summary of some relevant educational research on force and motion. The published research and indeed our own mini research amongst year 12 and 13 students revealed that, despite our best efforts as A-level teachers, significant numbers of students were leaving our classes with erroneous ideas about force and motion, ideas which we had thought we had taught well and ideas which had surfaced repeatedly throughout the education process. The message to our audience was simply that between us from Key Stages 1 to 5 we just haven't managed to crack the basics. And by 'crack the basics' we mean change intuitive ideas about force and motion into 'scientific' ideas.

We recognize that forces appear in a number of disguises within science: magnetic, nuclear, intermolecular, gravitational etc. We narrowed our work down to looking simply at objects in motion and at rest. The arch enemy, so to speak, in this arena is the lesser known law of obvious momentum. This states that everything that is moving must have a forward force known often as 'the obvious momentum' or 'its own forward force' or 'the force you gave it'. This intuitive hard nut can be found in many research references [1, 2] and is often referred to as the 'impetus' idea. Figure 1 shows typical student responses when invited to draw the forces on a stone being moved in a vertical circle on the end of a length of string. A recent A-level exam question set a similar task.

Figure 1. Typical responses of post-16 students when asked to draw arrows to show the force(s) acting on the stone in the position shown.

Our own research was based on a set of nine free body diagrams given to students who were following a two-year physics course at A-level in our respective institutions. We based our questionnaire on an article by Peter Whiteley in a recent issue of Physics Education [3] and our work extends and complements his findings. The students covered a broad range of potential from mean GCSE scores of 4.5 to 7.0. In figure 2 we include the results from just two questions from the nine on our question sheet.

Figure 2. In questions 5 and 7 students were asked to draw arrows to show the force(s) acting on the stone in each case. The tables give the range of responses with the correct response ticked.

The results of year 12 students in their first term of an advanced physics course and having yet to cover mechanics in the course represent what a keen KS4 student might suggest. To question 5 fewer than 25% correctly identify the two forces acting whilst more than 75% identify an 'intuitive' forward force. It is a major concern to us that year 13 students do not fare much better, they having been taught a ten-week module on mechanics (force and motion).

To question 7 once again the effect of tuition we have given between years 12 and years 13 is evident but still only about one third of the respondents gave the correct answer in year 13.

Some ways forward

(1) There is something to be said for looking at the language we use in talking about motion. Force is clearly a difficult concept. However 'energy' or even 'momentum' if used in place of force by pupils would make more sense, e.g. 'The trolley moves until all the force (energy/momentum) you gave it gets used up.' Perhaps we should encourage the use of 'energy' or 'momentum' or 'motion' in younger pupils without worrying about strict definitions of these terms. If intuition wants to ascribe something to the ball, let's give young people a more correct word to use. (If you can't beat them, join them).

(2) What exactly is the force? When we kick a ball is the force the leg? is it in the leg? is it in the ball? 'Where exactly is the force?' was the subject of a conversation between us and two primary school teachers. They were puzzled as to how they should best describe what the force was or where it was in such a case. The best advice we could offer was to stop thinking of the force as a thing. It can't be labelled like a banana. It is more like an action, a verb rather than a noun. I encouraged them to talk about 'forcing' rather than 'the force' and in so doing were immediately reminded of the debate about another process effecting change - 'heat' and 'heating'. As a last word on the use of language it might be helpful to reflect on what message we convey when we talk about 'giving the trolley a push'. If we have 'given it a push' they clearly it has the push we have given it.

(3) Do ticker-timers really work? Or for that matter electronic timers? Yes, they can have a part to play but they don't seem to get to the heart of the cognitive problem. They don't crack the nut, they just package it. The research findings support our view that we need to build more time into our teaching for reflecting on and talking about movement and forces, more time to look at simple questionnaire responses such as those in figure 2. For our A-level classes we are going to build the free body force questions into our teaching programme and use them as discussion points. But more influential than just sharing research findings with year 12 students might be to get students to actually carry out their own mini research project using similar simple free body diagrams. They might gather data from friends and family but also from younger pupils in lower years and so start to recognize and reflect on the origin of their own misunderstandings.

We had a slight concern before the presentation that our own preoccupation with post-16 students might make the presentation less than interesting to primary phase teachers. However, after the event we received considerable thanks and support from two primary teachers in particular, who encouraged us to present the same talk at other Key Stage 2 Inset events on forces. Our thanks go to them and to all who braved the elements to support us and Physics Education.

Bob Kibble and Becky Parker

References

[1] Driver R, Guesne E and Tiberghien A 1985 Children's Ideas in Science (Milton Keynes: Open University Press)

[2] Driver R, Squires A, Rushworth P and Wood-Robinson V 1994 Making Sense of Secondary Science (London: Routledge)

[3] Whiteley P 1996 Using free body diagrams as a diagnostic instrument Phys. Educ. 31 309 - 13

[4] Trumper R and Gorsky P 1996 A cross-college age study about physics students' conceptions of force in pre-service training for high school teachers Phys. Educ. 31 227 - 36