All lessons › Solids, liquids and gases › Lesson 3
Australian primary science · Year 5 · Lesson 3 of 3
Smells on the move
Inquiry question: How do gases spread, and what happens when a gas warms up?
Check practical materials
Testing an idea
What students learn
Gas particles move fast in all directions, so a gas spreads out through the air. Warming a gas makes its particles move faster and push harder, so the gas expands.
Success criteria
- I can record when a smell reached my table.
- I can predict and observe what happens to a balloon when the air in a bottle warms and cools.
- I can explain my observations using moving particles.
Preparation and materials
Before this lesson: Students know gases spread to fill their container and can be squashed (lesson 2).
- Vanilla essence (or a freshly cut orange), in a cup with a lid or cover — 1
- Empty small plastic drink bottles (about 600 mL), lids off — 13
- Balloons (latex-free if anyone has a latex allergy) — 13, plus spares
- Bowls or ice-cream tubs — 26 (2 per pair)
- Warm tap water (comfortable to touch, not boiling) — Enough for 13 bowls
- Cold tap water, with ice cubes if available — Enough for 13 bowls
- iPad timer or classroom clock with a second hand — 1
- Towels for spills — 13
Teacher setup
- Check for allergies or sensitivities to vanilla, orange or latex before the lesson.
- Arrange tables at different distances from the front of the room, and close windows and doors.
- Stretch each balloon a few times so it inflates more easily.
- Fill bowls just before Part B: one warm and one cold per pair.
Safety and adaptations
- Check allergies first: anyone sensitive to scents sits near an open door or is the timer. Use no perfume sprays or aerosols.
- Use warm tap water only, never boiling water. The teacher fills the warm bowls.
- Use latex-free balloons if anyone has a latex allergy.
- Put broken balloon pieces in the bin straight away; they are a choking risk.
- 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.
- Part A: predict which tables will smell the vanilla first.
- The teacher opens the vanilla and starts the timer. Each pair records the time they first smell it, and their distance from the cup.
- Part B: stretch a balloon over the neck of an empty bottle.
- Predict, then stand the bottle in warm water for 2 minutes. Observe the balloon.
- Move it into cold water for 2 minutes and observe again.
- Explain each result using particles.
Teacher modelling prompt
For Part A, think aloud: “I predict the tables closest to the vanilla smell it first, because the particles have less distance to travel. I’ll open the cup and start the timer. Raise your hand when you first smell it, and I’ll call out the time.” For Part B, model fitting a balloon over the bottle’s neck without blowing into it.
Record and explain evidence
Recording question: How do gases spread, and what happens when a gas warms up?
| Test | Prediction | What we observed (time, distance or balloon size) | Particle explanation |
|---|---|---|---|
| ________________ | ________________ | ________________ | ________________ |
Example recording headings; record actual observations, including inconclusive results.
Discussion prompt
The particle model says particles don’t change size. Whose explanation fits?
Check understanding
What should pupils know? Why did the smell reach the closest tables first?
Explain with evidence: Explain why the balloon shrank when the bottle went into cold water.
Apply the idea: Why do gas companies add a smell to natural gas?
Teacher answer guidance and saved classroom work are available through the main lesson experience where supported.