Ngā Hihiri · Energy
Transfers, transformations, and efficiency · Years 9–10
Ngā Whāinga Akoranga · Learning Intentions
- Identify and classify different types of energy and describe energy transfers and transformations.
- Apply the law of conservation of energy to explain that energy cannot be created or destroyed.
- Define work and calculate it using force and distance.
- Calculate energy efficiency and represent energy flows using energy diagrams.
- Explain energy transformations in biological systems and combustion engines.
Paearu Angitu · Success Criteria
- I can name at least six types of energy and classify them as kinetic or potential.
- I can explain the law of conservation of energy and apply it to identify all energy outputs in a system.
- I can calculate efficiency using efficiency = (useful energy output ÷ total energy input) × 100%.
- I can draw and interpret an energy flow diagram showing energy inputs, useful outputs, and wasted energy.
- I can trace energy through biological systems (digestion, photosynthesis) and combustion engines.
Hononga Marautanga · Curriculum Connections
This activity addresses the following Science curriculum statements (Draft 2025, Phase 4 — Years 9, 10):
- Energy: Energy is a quantifiable property of a system that is conserved and can be calculated based on the state of the system.
- Types: Energy in a system may be associated with motion (kinetic), position (potential), heat (thermal), light, sound, chemical bonds, or electrical fields.
- Kinetic: Kinetic energy is associated with motion, including the energy of moving objects and the random motion of particles (thermal energy).
- Potential: Potential energy is associated with the position or configuration of a system, including gravitational, elastic, and chemical potential energy.
- Unit: Energy is measured in the standard unit Joule (J).
- Work: Work is done when a force causes an object to move in the direction of the force, resulting in energy transfer. Work is measured in Joules.
- Conservation: The law of conservation of energy states that energy cannot be created nor destroyed, but can be transferred or transformed.
- Transfers: Changes in the natural and human world involve the transfer and transformation of energy between different forms.
- Efficiency: Energy transfers and transformations are not 100% efficient — some energy is always dispersed as heat to the surroundings.
- Efficiency: Energy efficiency is the percentage of input energy that is usefully transferred or transformed.
- Efficiency: The overall energy efficiency of a series of transfers or transformations can be calculated by multiplying individual efficiencies.
- Diagrams: Energy diagrams are used to model the transfer and transformation of energy and to represent conservation of energy.
- Combustion: Combustion of fuels involves chemical reactions that release energy stored in molecular bonds.
- Engines: In combustion engines, the increase in thermal energy causes gases to expand rapidly, performing work to drive pistons and wheels.
- Rockets: In rockets, combustion increases the temperature and pressure of gases, which are expelled to produce thrust.
- Biological: When food is digested, energy stored in chemical bonds is released and used to support the body's functions.
- Biological: Photosynthesis involves a transformation of energy from sunlight into chemical energy stored in glucose.
- Historical: James Prescott Joule (1818–1889) quantified the relationship between heat and mechanical work, establishing the mechanical equivalent of heat.
- Historical: Julius Robert von Mayer (1814–1878) established the mechanical equivalent of heat, linking different forms of energy.
- Historical: William Thomson (Lord Kelvin, 1824–1907) defined absolute temperature and helped formulate the second law of thermodynamics.
- Historical: William Pickering (1910–2004) was a New Zealand-born rocket scientist who directed NASA's Jet Propulsion Laboratory.
Wāhanga 1 · Types of Energy
Energy is a quantifiable property of a system — it can be measured, calculated, and tracked. The standard unit of energy is the Joule (J), named after James Prescott Joule. All types of energy fall into two broad categories: kinetic (energy of motion) and potential (stored energy).
- Mechanical: moving objects (ball, car, waka)
- Thermal: random motion of particles (heat)
- Sound: vibrations travelling through matter
- Light: electromagnetic radiation
- Electrical: moving charges (current)
- Gravitational: position above the ground
- Elastic: stretched/compressed spring or rubber band
- Chemical: stored in molecular bonds (food, fuel, batteries)
- Nuclear: stored in atomic nuclei
Classify each example — type of energy and kinetic or potential:
| Example | Specific energy type | Kinetic or Potential? |
|---|---|---|
| A hāngi stone being heated | ||
| A waka at the top of a waterfall | ||
| Glucose in a kūmara | ||
| Sound of a pūkāea (wooden trumpet) | ||
| A compressed pounamu spring toy |
Wāhanga 2 · The Law of Conservation of Energy
Total energy in = Total energy out (always)
Energy moves between objects (transfer) or changes from one form to another (transformation). In practice, every transformation produces some wasted thermal energy — perfect efficiency is impossible.
Same type of energy moves from one object to another.
e.g. hot stone heats the water → thermal energy transferred
Energy changes from one form to a different form.
e.g. chemical energy in kārearea muscles → kinetic energy of flight
Trace the energy transformation chain for each scenario:
| Scenario | Energy chain (use arrows: →) |
|---|---|
| A taiaha (staff) thrower prepares and strikes | |
| A solar panel charges a battery | |
| A petrol engine drives a car | |
| Photosynthesis in a harakeke (flax) plant |
Work: Work (W) is done when a force (F) moves an object a distance (d) in the direction of the force. W = F × d. Work is measured in Joules (J). A force that does not cause movement does no work.
Wāhanga 3 · Efficiency and Energy Diagrams
No energy transformation is perfectly efficient. Some energy is always lost to the surroundings as thermal energy (heat). The efficiency of a system tells us what proportion of the energy input is usefully converted.
| Device | Energy in (J) | Useful energy out (J) | Wasted as heat (J) | Efficiency (%) |
|---|---|---|---|---|
| LED light bulb | 100 | 90 | ||
| Incandescent bulb | 100 | 5 | ||
| Petrol car engine | 1000 | 750 | ||
| Solar panel | 500 | 100 |
Energy flow diagrams (Sankey diagrams):
Energy diagrams show ALL energy flows — inputs, useful outputs, and wasted energy. The total width of arrows at the output must equal the input (conservation of energy). Draw a Sankey diagram for a petrol car engine (1000 J in → 250 J kinetic + 750 J heat):
Wāhanga 4 · Energy in Biological Systems and Engines
Plants transform light energy from the sun into chemical energy stored in glucose (C₆H₁₂O₆).
Energy transformation: light → chemical potential energy
When food is digested, chemical energy stored in bonds is released through respiration to power movement, growth, and repair.
Energy transformation: chemical → kinetic + thermal
Burning fuel releases thermal energy, causing gases to expand rapidly. This expansion drives pistons, converting thermal energy to kinetic energy of the vehicle.
Chemical → thermal → kinetic (+ heat losses)
Typical efficiency: only ~25% of fuel energy → useful motion.
In rockets, combustion rapidly increases the temperature and pressure of exhaust gases, which are expelled backward at high speed — producing thrust forward (Newton's 3rd Law).
Chemical → thermal + kinetic (exhaust) → kinetic (rocket)
William Pickering (1910–2004), born in Havelock, NZ, directed NASA's JPL and led the first successful US satellite launch (Explorer 1, 1958).
Tūhono Aotearoa · New Zealand Connections
Aotearoa generates about 17% of its electricity from geothermal sources — chemical and thermal energy stored deep in the earth converted to electrical energy. Māori at Whakarewarewa have used geothermal energy for cooking and heating for centuries, understanding energy transfer long before Western science formalised it.
The Waikato River drives eight hydroelectric power stations, generating about 4,000 GWh per year. Energy transformation: gravitational potential → kinetic (water flow) → kinetic (turbine) → electrical. Te Whanganui-a-Tara Wellington is investigating tidal energy at Cook Strait — an emerging source of kinetic energy conversion.
Rocket Lab, founded in New Zealand, launches small satellites from the Māhia Peninsula. The Electron rocket burns liquid oxygen and kerosene — a chemical energy source. This continues the legacy of William Pickering, whose rocket science pioneered space exploration from NZ roots.
The Maramataka guides planting, harvesting, and fishing by observing natural energy cycles — solar energy driving plant growth (photosynthesis), tidal energy affecting fish movement, thermal energy from seasons driving migration. This holistic understanding of energy flow in nature reflects deep mātauranga Māori.
Whakaaro Hōhonu · Deeper Thinking
- A 60 kg student climbs a staircase 4 m high. How much gravitational potential energy do they gain? (Use E = mgh, where g = 10 m/s²). Where did this energy come from?
- A power station burns coal (chemical energy) at 35% efficiency and the electricity grid loses 8% of that in transmission. What percentage of the original coal energy reaches your home? (Multiply efficiencies: 0.35 × 0.92)
- Why does eating kūmara (sweet potato) give you energy? Trace the complete energy chain from sunlight to running on a sports field.
- Extension: New Zealand aims to be 100% renewable electricity by 2030. Which energy transformations are involved in: (a) wind power, (b) tidal power, (c) solar panels? For each, identify what is lost as waste heat and why 100% efficiency is thermodynamically impossible.
Kuputaka · Key Vocabulary
Kaiako Planning Snapshot
Resources already provided. What to print: this handout (2 pages). All activities are self-contained — no additional photocopying required.
Classroom use: Works as a starter, formative check, or paired investigation. Linked next step: Te Wānanga for a differentiated lesson plan, or save to My Kete.
NZ pedagogy basis: Aligned to Te Mātaiaho (Draft 2025) and Tātaiako cultural competencies. Suitable for all NZ kura and schools.
Mō ngā kaiako — For teachers and ākonga:
Inclusion: ESOL / ELL ākonga — bilingual headings and visual supports built in. UDL / neurodiverse learners — chunked sections, multiple representation formats. ADHD-friendly: short, scaffolded tasks with clear structure.
Differentiation: Entry-level tasks use supported sentence frames; on-level tasks are open-ended; extension tasks require abstract reasoning. Scaffold down with word banks; stretch by removing structured supports.