1
Squash and stretch
Workbook 2: Topic 2.2, pp. 22–24
GoalSay that a push can squash a soft object and a pull can stretch it, so a force can change its shape.
New words
force · a push or a pullshape · how an object looks round its edge, such as long, flat or roundsquash · to push something so it gets flatter or smallerstretch · to pull something so it gets longer
Explanation
A force can change the shape of an object. If you push a sponge in your hand, it gets squashed and smaller. If you pull both ends of a wool scarf, it gets stretched and longer. A balloon stretches when you blow it up. Soft things are easy to squash and stretch. Hard things like a rock or a brick do not change shape when you push them with your hands. When you stop squashing a sponge it often springs back, but a lump of dough stays squashed.
Worked examples
Nodira pushes down on her soft teddy with both hands. The teddy gets flatter. The push has squashed it.
Kenji holds a long piece of wool at both ends and pulls. The wool gets longer. The pull has stretched it.
A hard brick stays the same shape, however hard a child pushes it. Not every object can change shape.
Class activity
Soft or hard? (with an adult): collect six things from home, such as a sponge, a sock, a spoon, a pillow, a coin and a ball of dough or wool. Push or pull each one gently. Sort them into two piles: “changes shape” and “stays the same”. Put the things away tidily.
Practice
1
Which of these can you squash easily with your hand?
A, the soft bread.
2
Ana pulls both ends of a sock. Does the sock get squashed or stretched?
Stretched. It gets longer.
3
Is squashing a sponge done with a push or a pull?
A push.
4
Name one object that does not change shape when you push it with your hands.
For example: a rock, a brick, a spoon or a coin.