A five-minute opening
- Open the lamp example. Hide values and ask what each branch represents.
- Reveal the values. Check 100 J = 20 J + 80 J.
- Show the grid: one square represents 10 J. Count thicknesses of 10, 2 and 8 squares.
- Reveal efficiency, then adjust the useful fraction. The total remains conserved.
- Open Learn to draw and construct the same account together.
The physics behind the picture
Width, measured perpendicular to an arrow, represents energy or power. Length and arrowhead area have no numerical meaning. Colours identify branches; they are not physical properties.
A complete account uses one system boundary and one interval. Input equals outputs when there is no unrepresented retained-energy change. Include any retained energy explicitly in a custom account. “Wasted” energy is still present, usually spread into less useful thermal stores.
Usefulness depends on the stated purpose. Sound can be useful in a loudspeaker. Heating can be useful in a heater. Light, sound and electrical transfer are pathways, not energy stores.
Curriculum
AQA GCSE Physics 8463: 4.1.1.1, 4.1.1.4 and 4.1.2.1–4.1.2.2. Combined Science: Trilogy 8464: 6.1.1.1, 6.1.1.4 and 6.1.2.1–6.1.2.2. Conservation and efficiency underpin the suite; Sankey diagrams are a teaching representation and are not explicitly named in the AQA Physics specification. The statement about describing ways to increase the efficiency of an intended transfer is marked Higher Tier in AQA.
AQA Physics specification ↗ · AQA Combined Science content ↗
Model and drawing limits
Values are illustrative, not calibrated device data. Adjusting efficiency edits an energy account; it does not simulate the internal mechanism of a machine. There is one input and up to four outputs. Each output is counted once. Multi-stage chains and heat-pump coefficient of performance are outside this version.
Guided drawing checks widths and chosen labels. Small quantities keep their correct width; use browser zoom or a smaller grid scale to inspect them. A grid square is an on-screen unit, not a promise of a physical centimetre when printed. Percentage comparisons show a separate normalised scale.
Controls and recovery
Drag a round handle in Build or Learn to draw to change a width. Numeric fields provide the same action without dragging. Escape cancels a drag. Undo and Redo restore account and drawing edits. Ctrl+Z / Ctrl+Shift+Z work when focus is outside text fields.
Present enlarges the diagram; Controls reopens the inspector. Fullscreen is optional. Dialogs close with Escape. On a small screen the diagram can scroll horizontally, and Controls opens the activity sheet.
Save on this device keeps one account and its display settings in this browser. JSON files can be reopened. Examples, reset and imports are undoable. Export uses the current display settings; pupil exports hide numerical values. The suite contains no pupil accounts or assessment tracking.
Current example
