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Australian primary science · Years 5–6 · Lesson 1 of 6
The particle puzzle
Inquiry question: Why does the outside of a cold drink can get wet on a warm day?
Check practical materials
Observing
What students learn
Solids, liquids and gases behave differently because their particles are arranged and move differently.
Success criteria
- I can describe how particles behave in solids, liquids and gases.
- I can record and compare observations of two cold cups at the same times.
- I can use evidence to explain where water droplets on the outside came from.
Preparation and materials
Before this lesson: Students know the three states of matter (solid, liquid, gas).
- Two identical clear cups per pair — 26 cups for 13 pairs
- Ice cubes (equal amounts for both cups) — 26 portions (2 per pair)
- Water — A small, equal amount for each cup
- Table salt (1 tablespoon for cup B) — 13 tablespoons (1 per pair)
- Measuring spoons — 13
- Food colouring (optional; equal amount in each cup) — 1 bottle
- Paper towel (to dry both cup outsides) — 13 sets (1 per pair)
Teacher setup
- Freeze enough ice for two cups per pair. Use matching cups so only the added salt differs.
- Set out one tablespoon of salt per pair. Use a small, equal amount of water in each cup.
- Print a comparison investigation record per pair if using paper. Check that the room is warm enough for condensation to become visible.
Safety and adaptations
- Do not touch or hold the very cold ice-and-salt mixture against your skin.
- Wipe up water spills promptly to prevent slips.
- Do not taste the ice, salt or water.
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.
- Label two identical cups A (ice) and B (ice + salt). Put the same amount of ice and a little water in each. Add the same few drops of food colouring to both if using it.
- Add one tablespoon of salt to cup B only and stir. Dry the outside of both cups. Place them side by side in the same location.
- Record the outside of each cup at 0, 2, 4, 6, 8 and 10 minutes. In the same table row, note when droplets appeared and how much water you can see on each cup.
- Compare the two columns: which cup became wet sooner, or collected more droplets? Note if there was no clear difference.
- Use the evidence, including whether outside droplets are coloured, to distinguish observations from interpretations and explain where the water came from.
Teacher modelling prompt
Show two matching cups labelled A and B. Both contain equal ice and a little water; only B has a tablespoon of salt stirred in. Dry their outsides. Model a 0-minute observation for each cup, keeping what is seen separate from an explanation. Ask which cup students think will develop droplets first, and why.
Record and explain evidence
Recording question: How does adding salt to ice change the droplets on the outside of a cup?
| Time (min) | Cup A · ice: outside droplets | Cup B · ice + salt: outside droplets | What is different (or the same)? |
|---|---|---|---|
| ________________ | ________________ | ________________ | ________________ |
Example recording headings; record actual observations, including inconclusive results.
Discussion prompt
What similarities or differences did you record, and what do they tell you about where the droplets came from?
Check understanding
What should pupils know? Describe how particles are arranged and move in ice and in liquid water.
Explain with evidence: How did the two cups compare? Use one observation from each cup to explain condensation.
Apply the idea: Why does a bathroom mirror fog up after a hot shower?
Teacher answer guidance and saved classroom work are available through the main lesson experience where supported.