Sankey diagramm

In teaching energy the BEST resources have adopted a framework based on ‘energy stores’ and ‘energy pathways’ which is advocated by, amongst others, (Boohan, 2014), (Millar, 2014) and (Tracy, 2014). As Millar (2014) says, this approach “is not perfect - but it is adequate and significantly better than [approaches] based on lists of ‘forms of energy’.” A clear guide to this approach can be found on the Institute of Physics’ website (Institute of Physics).

Energy transfers can be represented with box and arrow diagrams that clearly show the different energy stores and the ways in which the energy is transferred (these energy diagrams are used in the response activity: Energy stores circus and in the second progression toolkit for this key concept). Sankey diagrams do not show the ways that energy is transferred, but they do show the relative amounts of energy transferred in different ways. (Millar, 2011) also notes that Sankey diagrams imply conservation of energy.

In a study of students aged 12-14 (Duit, 1981) found that, even after teaching, very few students use ideas of the conservation of energy to explain their predictions about unfamiliar events. This question requires students to consider the dissipation of energy into heat stores and the conservation of energy to analyse events.

A summary of the BEST approach to teaching energy can be found on the Best Evidence Science Teaching home page which is on the STEM Learning website (Fairhurst, 2018).

Students should complete the question individually. This could be a pencil and paper exercise, or you could use an electronic ‘voting system’ or mini white boards and the PowerPoint presentation. The answers to the question will show you whether students understood the concept sufficiently well to apply it correctly.

Differentiation

You may choose to read the questions to the class, so that everyone can focus on the science. In some situations it may be more appropriate for a teaching assistant to read for one or two students.

1. B 2. C

In question 1:

Answers A and C begin with Liam’s motion and indicate that students may be linking energy to forces and motion. B and D both show the correct energy stores, and students need to consider relative amounts of energy transferred to different stores. At this stage they are unlikely to have any idea of what these proportions are. D shows equal proportions of energy transferred to each energy store, diagram B is a more realistic representation. Students may select D if they do not understand that the width of the arrows is proportional to the amount of energy transferred (although this thinking will mean that answer B is also picked half of the time).

In question 2:

Answers A and D do not show one of the heat stores. Answer B does show the correct energy stores, but too big a proportion going to the kinetic store. Students choosing this answer may not have noticed the 20% efficiency label, or they may not understand what this means. Alternatively, selecting this answer may indicate that students are simply not using the understanding that the width of the arrow is in proportion to the amount of energy.

If students have misunderstandings about selecting the Sankey diagram with the correct energy stores, it can be helpful to talk through a few examples in which, through class discussion, all the energy stores are identified. Students can then practise more examples, working in pairs or small groups, to help consolidate understanding through dialogue.

If students have misunderstandings about relating the width of the arrow to the relative amount of energy that is transferred, then giving them examples to draw can be helpful. For most students at this stage, drawing Sankey diagrams to scale is challenging and uses maths skills that are more advanced than they may have been taught in their maths lessons. It will probably be appropriate to use phrases such as ‘most of the energy’ or ‘a tiny bit of the energy’.

The following BEST ‘response activities’ could be used in follow-up to this diagnostic question:

• Response activity: Energy stores circus

Boohan, R. (2014). Making sense of energy. School Science Review, 96(354), 11.

Duit, R. (1981). Students' notions about energy concept - before and after physics instruction. In Jung, W., Pfundt, H. & Rhoneck, C. v. (eds.) Proceedings of the International Workshop on Problems Concerning Students' Representation of Physics and Chemistry Knowledge. Ludwigsburg: Pedagogische Hockschule.

Fairhurst, P. (2018). Teaching Energy. [Online]. Available at: https://www.stem.org.uk/best-evidence-science-teaching.

Institute of Physics. Supporting Physics Teaching (SPT): Energy [Online]. Available at: http://supportingphysicsteaching.net/EnHome.html [Accessed July 2018].

Millar, R. (2011). Energy. In Sang, D. (ed.) Teaching Secondary Physics. London: Hodder Education.

Millar, R. (2014). Teaching about energy: from everyday to scientific understandings. School Science Review, 96(354), 6.

Tracy, C. (2014). Energy in the new curriculum: an opportunity for change. School Science Review, 96(354), 11.