🧺 Te Kete Ako

The Physics of Hāngī

The Physics of Hāngī · Years 7–10

Ingoa / Name

Akomanga / Class

Rā / Date

Year LevelYears 7–10

TypeStudent handout — classroom resource

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.

$ $E = m c Δ T$ $

Where $E$ = Energy (Joules), $m$ = mass (kg), $c$ = specific heat capacity, $Δ T$ = 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 ( $c = 840 J / k g^{\circ} C$ ). You heat them from $20^{\circ} C$ to $600^{\circ} C$ in the fire.

Calculate the temperature change ( $Δ T$ ).
Calculate the total thermal energy stored in the stones ( $E = m c Δ T$ ).
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

Curriculum alignment for this handout has not yet been verified against the live curriculum statements. A generated placeholder that stood here was removed on 2026-08-29 because it matched no real statement.

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.

Curriculum alignment

NZC (2007) · Science essence statement: Science is a way of investigating, understanding, and explaining our natural, physical world and the wider universe. It involves generating and testing ideas, gathering evidence – including by making observations, carrying out investigations and modelling, and communicating and debating with others – in order to develop scientific knowledge, understanding, and explanations.
Pairing chosen by this resource: This resource chooses to teach that science alongside mātauranga Māori, which stands as a knowledge system in its own right — the pairing is this resource's own approach, not a quotation from the curriculum.
Focus of this resource: Understand how different knowledge systems — including mātauranga Māori — shape how communities relate to the natural world.