Real systems pass energy through many steps. A flow diagram follows it from start to end: a box for each stage, an arrow for each transfer or transformation, and side arrows for every by-product. Tracing all the outputs, useful and not, is how you find out where energy goes.
A coaster's second hill is always lower than its first. Designers have no choice. Why?
You can tell transfers from transformations. This lesson follows energy through whole systems.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: the second hill
ExploreTry it on the board and compare what happens with your prediction.
Explore: a coaster and a fire
People have made fire by spinning a stick against a piece of wood for many thousands of years, including many First Peoples of Australia.
Try it yourselfYour edits are saved in this browser.
Run the coaster with friction to the end. Watch the red bar.
Use the board. This ticks when you get there.
Lighting a fire with a fire drill: complete the flow diagram, then Check.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: tracing systems
In your book: draw a flow diagram for the fire drill, from food to flame. Mark each arrow transfer or transformation, and add a side arrow for every by-product.
In a torch (battery, wires, bulb), useful output or by-product?
Light from the bulb
Heat from the bulb
Heat in the battery and wires
Elaborate TypicalUse the same idea in a new context.
Elaborate: from a dam to your lights
Try it yourselfYour edits are saved in this browser.
Complete the flow from a dam to the lights at home, then Check.
Use the board. This ticks when you get there.
Elaborate WiderUse the same idea in a new context.
Elaborate: the coaster that stops
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
Real systems pass energy through many stages: trace it one step at a time.
A flow diagram has a box for each stage, an arrow for each transfer or transformation, and side arrows for by-products.
Count every output, useful and by-product. By-products (mostly heat and sound) go to the surroundings; they are never destroyed.
For teachers
Students trace energy through multi-step systems, naming each stage's energy and every transfer, transformation and by-product, and construct and critique flow diagrams (AC9S8U05, nodes 5 and 6). About 26 minutes.
I can trace energy through a system with several steps.
I can draw a flow diagram with every by-product.
I can spot what is missing from someone else's flow diagram.
Before class
A concept tutorial for introducing or revising the idea. Set the width with ?width=minimum, typical (default) or wider. It closes Year 8 energy and sets up Year 9 conservation and efficiency.
Not hinge nodes; tracing every output is the skill Year 9 needs. The prediction (the lower second hill) shows why by-products matter.
Board notes: the coaster's friction is a steady 400 N while it moves, so the heat bar grows with distance. The fire-drill chain is simplified to four stages. Fire drills (a stick spun against a hearth board) have been used by many peoples, including many First Peoples of Australia; for local practice and knowledge, use local resources and community guidance.
Running the lesson
Engage: tally the predictions. 'Yes, same energy' ignores by-products; 'used up' calls them destroyed.
Explore: ask what the red bar would show if the ride went on for longer.
Explain: the 'what's missing' question is the critique skill; the sort checks useful versus by-product.
In your own words: the fire-drill flow diagram with side arrows.
The hard part (on purpose)
Finding every output. When a student's diagram looks finished, ask 'what would you feel or hear at each stage?' to find the by-products.
When students get stuck
A student says energy is used up going downhill. Ask: Where did the red bar's energy come from, and is the total line lower? Fix: It came from the car's energy; the total didn't change. It moved into the surroundings.
A student leaves sound out of a flow diagram. Ask: Is the system quiet? Fix: If you can hear it, some energy became sound: add it.
Stretch and support
Stretch: A pendulum swings lower and lower. Draw its flow diagram over several swings. (Gravitational potential ⇄ kinetic, with heat and sound leaving at each swing.)
Support: Give a flow diagram frame: three boxes, two arrows, and two empty side arrows labelled 'by-product'.
Where it leads
Next: Year 9, Where does the energy go? (conservation of energy, AC9S9U05).
In class: trace energy in a hand-crank torch or a bouncing ball (measure each bounce's height).
What each step is for
Engage: the second hill: Students who expect the car to reach the same height again haven't counted the by-products; tracing all outputs is the node.
Explore: a coaster and a fire: The coaster shows by-products growing over a run; the fire-drill chain traces a five-stage system with a by-product at nearly every step.
Explain: tracing systems: Naming the useful output and every by-product at each stage, and judging a diagram for completeness, is what a flow diagram is for.
Elaborate: from a dam to your lights: A hydro-electric system links four stages and two by-products, the full multi-step trace.
Elaborate: the coaster that stops: Following a system to the end shows where all the energy finally goes: heat in the surroundings.
Now you can
Trace energy through a system with several steps.
Draw a flow diagram with every by-product.
Spot what is missing from someone else's flow diagram.