Energy and Thermal Physics

Building Sankey diagrams

Classroom Activity for 11-14 Supporting Physics Teaching

What the Activity is for

The purpose of this activity is to introduce the conventions of, and pupils to acquire familiarity with, Sankey diagrams. These diagrams allow us to describe processes in terms of the rates at which energy is shifting down various pathways. Ultimately this will require calculations, but for now estimates are enough to get the conversations started. The interactive object allows you to build Sankey diagrams for a number of given situations, and then to construct your own.

There is an important choice to be made: you'll have to decide whether you want to talk about processes that:

  • are happening—so essentially about power and therefore best represented with Sankey arrows
  • have happened—so essentially about snapshot to snapshot, and so best represented with bars showing the quantities of energy

Because of this essential distinction, each resource is provided in two forms.

What to Prepare

  • a data projector or interactive whiteboard and this interactive object
  • access to these resources

Power suggestions

  • a car travelling along a motorway
  • a leaf photosynthesising
  • a bicycle freewheeling

Energy suggestions

  • a sprung toy which has jumped into the air
  • a bicycle which has freewheeled to a halt
  • a car which has braked to a stop

What Happens During this Activity

This activity should be conducted as a teacher-led interactive demonstration using a data projector. Discuss the various situations you choose and use the interactive object with pupils, guiding their views as to stores and pathways. Use the controls to implement your decisions for the values of the power, explaining that the thickness of the arrows in the Sankey diagram represents the power in the pathway.

By the end of the demonstration, pupils should be familiar with the key features of Sankey diagrams and be in a position to start sketching their own diagrams.

appears in the relation ΔEΔt>ℏ/2 ΔQ=mcΔθ E=hf E ∝ A^2
has the special case Photon Energy
is used in analyses relating to Emission/Absorption Spectra Phase Change
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