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Australian primary science · Years 3–4 · Lesson 2 of 6
Bend, stretch or snap?
Inquiry question: A bookmark needs to bend without breaking. Which material is best?
Check practical materials
Fair testing
What students learn
Materials differ in flexibility and strength, and we can test these properties.
Success criteria
- I can test how bendy a material is in the same way each time.
- I can record what I observed, not what I expected.
- I can use my results to choose a material for a job.
Preparation and materials
Before this lesson: Students can name materials and describe a property (lesson 1).
- Strips 2 cm × 15 cm of: paper, thin card, plastic (from a clean drink bottle), aluminium foil (folded twice), felt or cotton fabric; plus a jumbo craft stick (about 15 cm × 2 cm) — 1 of each per pair (78 pieces)
- Rulers — 13
- Masking tape — 2 rolls
Teacher setup
- Cut strips to the same size before the lesson.
- Make a demonstration set to model the test.
Safety and adaptations
- Cut plastic strips yourself before the lesson; edges can be sharp.
- Do not try to snap craft sticks. Stop when a sample resists bending or begins to crack; tell your teacher.
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.
- Tape each strip so 10 cm hangs over the edge of the desk.
- Observe and record: does it droop a lot, a little or not at all?
- Gently curve each flexible strip without forcing it. Record: springs back, stays bent or resists bending. Stop if it starts to crack.
- Do every strip the same way.
- Choose the best bookmark material using your evidence.
Teacher modelling prompt
Tape a paper strip to the edge of a desk so 10 cm hangs over. Say: “I observe the end droops to about 3 cm below the desk. I write ‘droops a lot, did not break’. I don’t write ‘it is weak’: that is a conclusion that needs a strength test, not what I directly observed.” Then bend it gently and record whether it springs back.
Record and explain evidence
Recording question: Which materials bend without breaking?
| Material | Droop (a lot / a little / none) | When gently curved (springs back / stays bent / resists bending) |
|---|---|---|
| ________________ | ________________ | ________________ |
Example recording headings; record actual observations, including inconclusive results.
Discussion prompt
Which claim uses evidence from our test?
Provided example or reference data
Illustrative sample observations (written for this lesson; not your own tests)
| Sample | Overhang | Gentle bend |
|---|---|---|
| Paper strip | 10 cm; drooped a lot | Stayed curved |
| Thin plastic strip | 10 cm; drooped a little | Sprang back |
| Craft stick | 10 cm; no obvious droop | Resisted bending; test stopped |
Check the data source in the teacher lesson. Illustrative or fictional data are not measurements collected by your class.
Check understanding
What should pupils know? What does flexible mean? Name one flexible material from today.
Explain with evidence: Mia wrote “the craft stick is rubbish”. Rewrite it as an observation.
Apply the idea: Which material would you use for a phone case that should bend a little but not crack: glass, rubber or foil? Why?
Teacher answer guidance and saved classroom work are available through the main lesson experience where supported.