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Australian primary science · Year 3 · Lesson 3 of 3
Warm meets cold
Inquiry question: What happens when something warm touches something cold?
Check practical materials
Observing
What students learn
When a warm thing touches a cold thing, heat moves from the warm one into the cold one. The warm one cools down and the cold one warms up. Heat moves through metal faster than through plastic or wood.
Success criteria
- I can describe what happens to warm water next to cold water.
- I can say which way the heat moved.
- I can explain why a metal spoon feels colder than a plastic or wooden one.
Preparation and materials
Before this lesson: Students know heat moves from hotter to cooler things (lessons 1 and 2).
- Small plastic cups — 13
- Bigger cups or small containers that the small cups fit inside — 13
- Warm tap water — Enough to fill 13 small cups
- Cold tap water (chilled in a fridge if you can) — Enough to half-fill 13 bigger cups
- Metal spoons — 13
- Plastic or wooden spoons — 13
- Thermometers, if your school has them — Optional, up to 26
- Timer — 1 per pair or the class clock
Teacher setup
- Leave all the spoons on a table for at least an hour so they are at room temperature.
- Just before the investigation, half-fill the bigger cups with cold water and fill the small cups with warm tap water. Check it feels comfortably warm, not hot.
- Print one investigation record per pair.
Safety and adaptations
- Use warm tap water only: no kettles or hot water for students.
- Teacher checks the water feels comfortably warm, not hot.
- Glass thermometers break easily: hold them gently and never stir with them.
- Wipe up spills straight away.
Review your school policies and curriculum requirements before teaching.
How to investigate
The lesson sequence should leave pupils with evidence to interpret, not only an activity to finish.
- Spoon test: each partner holds a metal spoon in one hand and a plastic or wooden spoon in the other. Which feels colder? Record it under the table.
- Predict what will happen when the small cup of warm water stands in the bigger cup of cold water.
- Dip a finger in each and record how they feel (and the temperature, if you have thermometers).
- Stand the warm cup inside the cold cup. Check both every 5 minutes for 15 minutes.
- Compare your results with your prediction.
Teacher modelling prompt
Hold up a warm cup and a cold cup. Think aloud: “I predict heat will move from the warm water into the cold water. So the warm water will get cooler and the cold water will get less cold.” Show how to dip one finger in each and use the words hot, warm, cool or cold.
Record and explain evidence
Recording question: What happens when something warm touches something cold?
| Time (minutes) | Warm cup feels (hot / warm / cool / cold) | Cold cup feels (hot / warm / cool / cold) | Warm cup (°C, if you have a thermometer) | Cold cup (°C, if you have a thermometer) |
|---|---|---|---|---|
| ________________ | ________________ | ________________ | ________________ | ________________ |
Example recording headings; record actual observations, including inconclusive results.
Discussion prompt
Who is right? How could we check?
Check understanding
What should pupils know? When warm water touches cold water, which way does heat move?
Explain with evidence: Why did the cold water feel less cold after 15 minutes?
Apply the idea: Why do saucepans have plastic or wooden handles?
Teacher answer guidance and saved classroom work are available through the main lesson experience where supported.