Science and Technology K–6 · Kindergarten
Which strip is strongest: hanging washers until it bends
Material World (NSW 2017); Science understanding, Chemical sciences (ACARA v9)
The idea
Materials differ in how much load they carry before they bend, and a count of washers makes that difference measurable.
What you need
- Strips 15 cm long and about 2 cm wide of: card, corrugated cardboard, thin plastic (cut from an ice-cream lid), a jumbo wooden craft stick (about 15 cm by 1.8 cm) and copy paper; a spare strip of each
- Two stacks of books about 15 cm tall, standing 10 cm apart on one table top, so the strip bridges the 10 cm gap between them with room for the cup to hang below it, and another book on each end of the strip to hold it down
- A paper cup on a string hook hung from the middle of the strip, and a stack of card sheets on the table top under the cup, built up until the empty cup hangs 2 cm above it (the bend limit)
- 40 identical steel washers (about 5 g each, weighed once on the class scale)
How to do it
- Predict which strip will hold the most washers and which the fewest.
- Lay the strip across the 10 cm gap between the two book stacks and weight each end with a book. Hang the empty cup from the middle and build the card stack under it until the gap is 2 cm.
- Add washers one at a time. Stop when the cup touches the card stack (that is the bend limit). Count the washers; if all 40 go in without the cup touching, record 40+.
- Repeat for each strip, then order the strips from strongest (most washers) to weakest and compare with the prediction.
- Fold a fresh card strip into a zigzag with the folds running along its length and test it again. Record the new count.
What you should see
The counts differ widely between materials, and the order is the class's result: a stiff strip may take all 40 washers without reaching the bend limit (record 40+), while a floppy one reaches it within the first few washers. It cannot reach the limit with the empty cup, because the 2 cm gap is set with the empty cup already hanging, so the 2 cm is the extra sag the washers are allowed to add. Folding the card into a zigzag with the folds running along its length raises its count, because the shape, not only the material, carries the load. The washer count multiplied by the washer mass gives the load in grams (for example 12 washers of 5 g is 60 g), plus the few grams of the cup. The learner knows it worked when a fresh strip of the same material gives a count within one or two washers of the first.
What changes
- What you change
- material of the strip; later, the shape of the card strip
- What you measure
- number of washers at the bend limit
- What you keep the same
- strip length 15 cm and width about 2 cm
- gap 10 cm
- cup hung from the middle
- same washers
- same 2 cm bend limit
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- Only the material matters, not the shape (the zigzag card holds more than the flat card).
- Folding paper makes it weaker.
Safety card
Hazards
- Washers dropping on toes
Controls
- Cup hung low over the card stack; washers kept in a tray; the book stacks stood well back from the table edge
Note
No chemicals or heat. Record the activity on the school's risk assessment (Primary School RiskAssess, Ecosolve Australia, riskassess.com.au).
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
- Science and Technology K-6 Syllabus (2017), NESA. Current syllabus; NESA's timeline is 2026 plan and prepare, 2027 start teaching the 2024 syllabus. Code read from the official syllabus document on 2026-09-22.STe-4MW-ST
- Science and Technology K-6 Syllabus (2024), NESA. Implementation from 2027, so this code describes the future syllabus. Code read from the outcomes page on 2026-09-22.STE-SCI-01
- Australian Curriculum v9AC9SFU03AC9SFI02AC9SFI03AC9SFI04
Sources
The pages the author read to write this activity.