2
Stiff or bendy?
Workbook 2: Topic 3.4, pp. 38–40
GoalTest how much different strips bend, measure in centimetres, and say which is stiffest and which is most flexible.
New words
stiff · does not bend muchflexible · bends easilymeasure · to find out how big or how far, using a ruler
Explanation
Aisha wants to find out how stiff or bendy four strips are. She lets each strip stick out over a table edge by the same amount. She puts one coin on the end of each strip. The end dips down. She measures how far it dipped with a ruler. A stiff strip dips only a little. A flexible strip dips a lot. She records every measurement in a table. The strip that dips least is the stiffest.
| Material of strip | How far it dipped (cm) |
|---|---|
| wooden stick | 1 |
| thin card | 3 |
| plastic strip | 5 |
| paper | 8 |
Worked examples
Aisha tested a wooden stick, thin card, a plastic strip and paper. The wooden stick dipped only 1 cm. It is the stiffest strip.
The paper strip dipped 8 cm. It is the most flexible strip.
Her block graph shows the same results. The tallest block is the strip that bent most.
Class activity
Dip test (with an adult): let strips of card, paper, plastic and a wooden stick (all about the same size) stick out 10 cm over a table edge, holding the other end under a heavy book. Put one coin on the end of each and measure the dip with a ruler. Record in a table.
Practice
1
Look at Aisha’s table. Which strip dipped the most?
The paper strip, 8 cm.
2
Yuki tests two plastic strips of the same length. Which one is stiffer? Why might that be?
| Strip | How far it dipped (cm) |
|---|---|
| thin plastic | 7 |
| thick plastic | 2 |
The thick plastic strip. It dipped less. Both are plastic, so its thickness made it stiffer.
3
Which material would be too bendy for a bookshelf?
C, rubber. It is flexible, so the shelf would bend and the books would slide off.
4
Aisha says the strip that dips most is the stiffest. Is she right?
No. The strip that dips most is the most flexible. The stiffest dips least.