The Physics of Hāngī
The Physics of Hāngī · Years 7–10
Ngā Whāinga Akoranga · Learning Intentions
- Investigate a significant question using evidence from multiple sources
- Analyse and evaluate information to form and support a reasoned position
- Connect learning to real-world contexts, including Aotearoa New Zealand settings
- Communicate understanding clearly and accurately for a specific audience
Paearu Angitu · Success Criteria
- I use at least two sources and can evaluate their credibility
- My position is clearly stated and supported by specific evidence
- I can connect my learning to at least one real-world Aotearoa context
- My communication is clear, organised, and appropriate for the audience
Whakataukī | Proverb
"He kohatu wera, he hāngī reka."
A hot stone, a delicious hāngī.
This simple proverb reminds us that the success of the hāngī depends on the quality and heat of the stones (whatu). Science explains why the stones matter.
🔥 The Physics of Hāngī
Heat Transfer, Heat Capacity, and Thermodynamics in Traditional Cooking
1. The Three Methods of Heat Transfer
A traditional hāngī uses all three methods of heat transfer to cook food perfectly underground. Can you identify where each happens?
1. Conduction (Whakawhiti Wera)
Heat moves through direct contact.
- In Hāngī: The hot stones touch the wet sacks/baskets, transferring heat directly to the food containers.
- Key Concept: Solids are better conductors than gases.
2. Convection (Piki Wera)
Heat moves through fluids (liquids and gases).
- In Hāngī: Steam! Water triggers steam which circulates through the food layers, cooking them moistly.
- Key Concept: Hot steam rises, carrying heat energy upwards.
3. Radiation (Pāhihi Wera)
Heat travels as waves (infrared).
- In Hāngī: The red-hot stones radiate intense heat energy into the pit even before the dirt covers them.
- Key Concept: No physical medium needed.
2. Specific Heat Capacity (Te kaha o te kōhatu ki te pupuri wera)
Why do we use volcanic rocks (andesite/basalt) and not river stones or sedimentary rocks?
Definition: Specific Heat Capacity ($c$)
The amount of energy required to raise 1kg of a substance by 1°C.
$$E = mc\Delta T$$
Where $E$ = Energy (Joules), $m$ = mass (kg), $c$ = specific heat capacity, $\Delta T$ = temperature change.
The Stone Comparison
| Stone Type | Qualities | Suitability for Hāngī |
|---|---|---|
| Volcanic (Basalt/Andesite) | High density, high heat capacity. Does not crack easily. | ✅ Excellent - Holds heat for hours. |
| Sedimentary (Sandstone) | Porous, contains water pockets. Low density. | ❌ Dangerous - Can explode when trapped water boils! |
| Metamorphic | Variable. | ⚠️ Caution - Depends on structure. |
3. The Thermodynamics of the Earth Oven
Why bury it? By covering the pit with soil, we create a sealed thermodynamic system.
- Insulation: The earth acts as an insulator, preventing heat from escaping into the atmosphere.
- Pressure: The trapped steam slightly increases pressure (like a pressure cooker), which can reduce cooking time and tenderize meat.
- Equilibrium: Over 3-4 hours, the stones, steam, and food reach thermal equilibrium.
🧪 Activity: Calculate the Energy
Scenario: You use 50kg of volcanic stones ($c = 840 J/kg^{\circ}C$). You heat them from $20^{\circ}C$ to $600^{\circ}C$ in the fire.
- Calculate the temperature change ($\Delta T$).
- Calculate the total thermal energy stored in the stones ($E = mc\Delta T$).
- If 1kg of chicken needs approximately 300,000 J to cook, theoretically how much chicken could you cook? (Ignorning heat loss).
Hononga Marautanga · Curriculum Alignment
Level 3–4: Investigate social, cultural, environmental, and economic questions; gather and evaluate evidence from diverse sources; communicate findings and reasoning clearly for different audiences and purposes.
Level 3–4: Read, interpret, and evaluate information texts; write clearly and purposefully for specific audiences; apply critical thinking skills to evaluate sources and construct well-reasoned responses.
Tuhia ōu whakaaro · Write Your Thoughts
Reflect on your learning. What was the most important idea? What question do you still have?
Aronga Mātauranga Māori
This resource sits within a kaupapa that recognises mātauranga Māori as a living knowledge system with its own frameworks, values, and ways of understanding the world. The New Zealand Curriculum calls for learning that reflects the bicultural partnership of Te Tiriti o Waitangi, which means every subject area has an obligation to engage authentically with Māori perspectives — not as cultural decoration but as substantive contributions to how we understand our topics. The concepts of manaakitanga (care for others), kaitiakitanga (guardianship), whanaungatanga (relationship and belonging), and tino rangatiratanga (self-determination) provide a values framework applicable across all learning areas, and all are relevant to the work in this handout.
Ngā Rauemi Tautoko · Resources already provided
This handout is designed to be used alongside other resources in the same unit. Related materials are linked in the unit planner. All content is provided — no additional preparation is required to use this handout in your classroom.
📋 Teacher Planning Snapshot
Ngā Whāinga Ako — Learning Intentions
Students will engage with this resource to explore the intersection of STEM disciplines and mātauranga Māori — understanding how Indigenous knowledge systems and Western science share complementary ways of knowing the world.
Ngā Paearu Angitū — Success Criteria
- ✅ Students can identify connections between mātauranga Māori and STEM concepts in this resource.
- ✅ Students can explain how dual knowledge systems strengthen understanding of natural phenomena.
Differentiation & Inclusion
Scaffold support: Provide concept maps or sentence frames to scaffold access for students at the entry level. Offer extension tasks exploring specific mātauranga Māori knowledge domains (e.g., tohu āhua rangi, rongoā, whakapapa o te taiao) in greater depth.
ELL / ESOL: Pre-teach key vocabulary in both te reo Māori and English — including domain-specific STEM terms. Bilingual glossaries and visual anchors support comprehension. Allow students to demonstrate understanding in their preferred language.
Inclusion: Tasks are designed for a range of readiness levels. Neurodiverse learners benefit from structured, chunked activities with clear success criteria. Use hands-on, inquiry-based formats where possible. Affirm the value of different ways of knowing.
Mātauranga Māori lens: Mātauranga Māori encompasses astronomy, ecology, navigation, agriculture, and medicine — systems of knowledge developed over centuries. This unit treats mātauranga Māori as epistemically equal to Western science, not supplementary. Bring kaitiakitanga as a guiding ethic: knowledge is held in relationship, not extracted.
Prior knowledge: Students benefit from baseline understanding of the relevant STEM domain. No specialist te reo Māori knowledge required — glossaries provided. Best used after introductory lessons or as a standalone exploration.
Curriculum alignment
- Nature of Science — Knowledge: Science is a way of investigating, understanding, and explaining our natural, physical world; mātauranga Māori offers complementary systems of knowledge that enrich scientific understanding.
- Identity, Culture, and Organisation: Understand how different knowledge systems — including mātauranga Māori — shape how communities relate to the natural world.