2
Strong, bendy or stiff?
Workbook 2: Topic 3.2, pp. 32–34
GoalSay whether a material is strong, flexible or rigid, and give an example.
New words
strong · does not break easilyweak · breaks easilyflexible · able to bend without breakingrigid · stiff, does not bend
Explanation
A strong material does not break easily when you push it, pull it or put heavy things on it. Metal and wood are strong. A weak material, such as thin paper, tears or breaks easily. A flexible material bends easily without breaking. Rope and wool are flexible. A rigid material is stiff and does not bend. A brick is rigid. Glass is rigid but it is not strong, because it breaks if you drop it.
Worked examples
Ravi’s school bag has a strong strap made of cloth. The strap can hold heavy books.
A skipping rope can bend into a loop. It is flexible.
A hammer has a metal head. The metal is strong and rigid, so it does not bend when it hits a nail.
Class activity
Strong or weak? (with an adult): hold a sheet of newspaper at two ends and try to pull it apart. Now roll it up tightly and try again. Ask: which is easier to bend, a thin paper strip, a ruler or a piece of string? Say which things are flexible and which are rigid.
Practice
1
Is a woolly scarf flexible or rigid?
Flexible. It bends and folds easily.
2
Which material is rigid: the wood or the fabric?
A, the wood. Fabric is flexible.
3
Aisha says glass is a strong material. Is she right? Why?
No. Glass is hard, but it breaks easily if it is dropped.
4
Sort these into the Venn diagram: a metal spoon, a rope, a glass, a wooden table. Which one goes in the middle?
Strong and rigid (middle): the metal spoon and the wooden table. Strong only: the rope (it is strong but flexible). Rigid only: the glass (it is rigid but breaks easily).