All lessons › Where does the water go? › Lesson 2
Australian primary science · Year 4 · Lesson 2 of 4
Cold cup drips
Inquiry question: Why does a cold cup get wet on the outside?
Check practical materials
Observing
What students learn
When water vapour in the air cools, it condenses back into liquid water droplets.
Success criteria
- I can observe condensation.
- I can explain where the droplets come from.
- I can name condensation in everyday life.
Preparation and materials
Before this lesson: Students know water can evaporate into water vapour (lesson 1).
- Metal or plastic cups — 26
- Ice and water — Enough for 13 cups
- Food colouring — 1 bottle
- Paper towel — 13
Teacher setup
- Add food colouring to the iced water so students can test if droplets come from inside.
- Fill cups carefully and dry the outside before starting. Metal or thin plastic cups work best.
Safety and adaptations
- Wipe spills.
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.
- Fill one cup with icy coloured water and one with coloured water that is not cold.
- Observe both cups at 2, 4, 6, 8 and 10 minutes.
- Wipe the outside with paper towel: is the water coloured?
- Record observations and explain.
Teacher modelling prompt
Wipe the outside of a coloured iced cup with white paper towel: “If the cup leaked, the towel would be coloured. It’s clear. So where did the water come from?”
Record and explain evidence
Recording question: Where do the droplets on a cold cup come from?
| Time (min) | Icy cup outside | Not-cold cup outside |
|---|---|---|
| ________________ | ________________ | ________________ |
Example recording headings; record actual observations, including inconclusive results.
Discussion prompt
What evidence from the colour test helps decide?
Check understanding
What should pupils know? What is condensation?
Explain with evidence: How do the colour and two-cup observations support an explanation for the droplets?
Apply the idea: Why does a bathroom mirror fog up after a shower?
Teacher answer guidance and saved classroom work are available through the main lesson experience where supported.