Conservation Energy Law

Overview

This is lesson 2 of 36 in the unit “Energy in Physical Systems”. Students build from the idea of energy transfer by learning and applying the Law of Conservation of Energy to a physical system and to everyday examples.

Learning intentions

Students will be able to:

• describe a physical system and changes in it using observable evidence
• use energy concepts (transfer and conservation) to explain changes in energy within the system
• calculate or compare energy changes using a suitable energy expression (where appropriate)
• communicate a clear explanation linking evidence to energy reasoning

Success criteria

Students can:

• I can describe the system, what changes, and what evidence shows that change.
• I can explain where energy goes (transfer and/or transformation) during the change.
• I can state that total energy in an isolated system is conserved and use this in an explanation.
• I can use numbers/diagrams (e.g., energy bar chart) to support my explanation.

Curriculum links

• AS92047 Demonstrate understanding of a physical system using energy concepts: describing a physical system, the change, and relevant energy concepts using evidence.
• AS92047 explain a physical system using energy concepts: explaining change using relevant energy concepts and evidence.
• Science learning area focus: understanding physical systems through energy concepts and relationships.

Lesson structure (50 minutes)

1. 0–5 min · Hook: “Where did it go?”

• Teacher shows a quick demonstration photo/video idea: a bouncing ball or roller coaster car slowing down while still “moving”.
• Students do a quick think: write one sentence answering “What has happened to the energy?”

2. 5–12 min · Mini-teach: Conservation of energy in systems

• Teacher defines an “isolated system” for classroom purposes, and introduces the Law of Conservation of Energy: total energy stays constant while it transfers/transforms.
• Students record a one-sentence rule and complete a simple “energy in → energy out” diagram for a chosen example (e.g., falling object).

3. 12–22 min · Guided model: Energy bar charts

• Teacher models an energy bar chart for a physical system (e.g., roller coaster: gravitational potential energy decreases, kinetic energy changes, thermal sound increases).
• Students sketch their own bar chart for the same system using teacher prompts: “What forms of energy are present? What evidence suggests each change?”

4. 22–35 min · Group task: Apply to a real-world scenario

• Teacher assigns groups one scenario card:
• Example A: kettle heating water
• Example B: skateboard going downhill and slowing on rough ground
• Example C: torch battery powering a bulb (electrical to light/thermal)
• Students identify: (1) system boundary, (2) what changes, (3) energy forms involved, (4) where energy transfers to, and (5) a conservation statement for the system.
• Teacher circulates using prompts: “What evidence do you have for the change?” “What energy form increases or decreases?” “Is heat/sound included inside your system boundary?”

5. 35–43 min · Calculation focus (short): compare energy change

• Teacher provides one lightweight calculation template (choose one that fits the scenario):
• For lifting: Ep = mgΔh and then compare to Ek
• For heating: E = mcΔT
• For electricity: P = VI with a short time estimate to find energy transfer (ΔE = Pt)
• Students complete either (a) a single energy change calculation or (b) a comparison using given values, then add a conservation explanation sentence.

6. 43–49 min · Share-out: Evidence-based explanations

• Teacher asks each group to share one “best” conservation explanation using a structure: System → Change → Energy transfers/forms → Conservation statement → Evidence.
• Students listen and use a checklist to identify strong evidence and clear energy reasoning.

7. 49–50 min · Exit ticket

• Students answer: “In one isolated system example, explain what stays constant and what can change.” (2–3 sentences)

Resources

• Scenario cards (roller coaster/skateboard/kettle/torch)
• Energy bar chart template (printed or digital)
• Calculator access (class set or student phones if permitted)
• Whiteboard/markers or slides
• Data cards for the chosen calculation values (m, Δh, c, ΔT, V, I, t as appropriate)
• Student science notebooks or worksheets
• Timer for group work and share-out

Assessment

• Formative checks:
• Teacher monitors group discussions for correct system boundaries and identification of energy transfers/forms.
• During bar charts, teacher checks whether students link changes to evidence and appropriate energy concepts.
• Exit ticket:
• Assesses whether students can state conservation for a system and explain what changes vs what remains constant.

Differentiation

• Support:
• Provide sentence starters: “The system is…”, “The change is…”, “Energy transfers from… to…”, “Total energy stays constant because…”
• Offer a partially completed energy bar chart for struggling students.
• Provide a worked example model on the board for the chosen scenario type (heating, lifting, or electrical).
• Extension:
• Ask high-performing students to include a “non-ideal” note (e.g., friction causing additional thermal energy) while still maintaining conservation within the system boundary.
• Require an additional calculation or a comparison of two stages (start vs end energies).
• EAL/SEN considerations:
• Use visuals (bar charts, arrows, energy icons) to reduce language load.
• Allow oral explanations during share-out; teacher prompts can translate key terms into student language as needed.
• Prior knowledge link:
• Refer back to students’ earlier understanding of energy transfer by insisting that conservation uses transfers and transformations, not “energy disappearing.”