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Physical ScienceMaterialsYear 3 Science

Materials: bendy, stretchy, hard, snappy and soaking

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What this lesson covers

  • Flexible materials bend and twist easily, most of all when they are thin
  • Elastic materials stretch and then spring back to their first shape
  • Rigid materials are hard to bend, and brittle ones snap or shatter
  • Absorbent materials soak up water; waterproof ones keep it out
  • Measuring how far a material stretches
  • Choosing the right material for a job
Key idea

What is a property?

  • A material is what a thing is made of.
  • Wood, plastic, glass, wool and paper are all materials.
  • A property is what a material is like.
  • Does it bend? Does it stretch? Does it snap? Does it soak up water?
  • We find out by testing it.
Key idea

Flexible: it bends

  • A flexible material bends or twists without breaking.
  • Paper, cloth, tinfoil and a plastic straw are flexible.
  • Thin things bend more easily than thick things.
  • One sheet of paper bends easily. A thick pile of paper does not.
Key idea

Elastic: it stretches and springs back

  • An elastic material stretches when you pull it.
  • When you let go, it goes back to its first shape.
  • A rubber band, a hair tie and a balloon are elastic.
  • Play dough stretches too, but it stays stretched. So play dough is not elastic.
Key idea

Rigid and brittle

  • A rigid material is hard to bend, stretch or break.
  • A wooden table leg and a metal spoon are rigid.
  • A brittle material does not bend. It snaps or shatters when you bend it or hit it.
  • A dry cracker, an eggshell and a glass cup are brittle.
  • Rigid and brittle are not the same. A metal spoon is rigid, but it does not shatter when you drop it.
Key idea

Try it: which property fits best?

Key idea

Soaks it up or keeps it out

  • An absorbent material soaks up water. A paper towel, a sponge and a cotton sock are absorbent.
  • A waterproof material keeps water out. A plastic bag, a raincoat and a gumboot are waterproof.
  • To test, put a drop of water on it.
  • If the drop sinks in, the material is absorbent. If the drop sits on top, it is waterproof.
Side view of two flat materials after a drop of water: on the paper towel the water has soaked in and spread, on the plastic the drop sits on top as a round bead
Key idea

Try it: absorbent or waterproof?

Worked example

Example: how far does it stretch?

  • Room 5 hung the same bag of marbles on three things. They measured each one before and with the bag.
  • How far did each one stretch?
ThingBeforeWith the bag
Rubber band8 cm12 cm
Hair tie6 cm9 cm
String10 cm10 cm
A rubber band beside a ruler: 8 cm long before, 12 cm long with a bag of marbles hanging on it, and a bracket showing the 4 cm stretch
  1. Rubber band: 12 cm − 8 cm = 4 cmnew length take away first length
  2. Hair tie: 9 cm − 6 cm = 3 cm
  3. String: 10 cm − 10 cm = 0 cmstring does not stretch
  4. The rubber band stretched the most, 4 cm
  5. With the bag off, the band went back to 8 cm, so it is elastic
Worked example

Example: the best material for a raincoat

  • A raincoat must keep rain out, and it must bend when you move your arms.
  • Which is best: paper towel, wool or plastic?
  1. Paper towel is absorbent, so the rain would soak in
  2. Wool is flexible, but it soaks up water
  3. Plastic is flexible and waterproof

Common mistakes

  • Play dough is elastic because it stretches.
    Elastic things go back to their shape when you let go; play dough stays stretched, so it is not elastic.
  • Hard things are always brittle.
    Brittle things snap or shatter. A metal spoon is hard and rigid, but it does not shatter.
  • The band reached 12 cm on the ruler, so it stretched 12 cm.
    The stretch is the new length take away the first length: 12 cm take away 8 cm is 4 cm.
Try it at home

The drip test

You need: a paper towel, a piece of plastic bag, an old cotton sock, a piece of tinfoil, a cup of water, a teaspoon, a tray

  1. Lay the four materials flat on the tray.
  2. Guess which ones will soak up water. Say your guess out loud.
  3. Put one teaspoon of water on each material.
  4. Count slowly to 20, then lift each one and look underneath.
  5. Look for where the water went. On absorbent materials it soaks in and spreads. On waterproof ones it sits on top in a round drop.

Safety: Ask an adult to help, and wipe up any spilled water straight away so nobody slips on the wet floor.

Your turn

1

A hair tie is 6 cm long. When it is stretched it is 10 cm long. How far did it stretch?

2

You bend a dry cracker and it snaps. Is it flexible or brittle?

3

Which is best for a bath mat: plastic, a towel or glass?

4

A balloon is blown up, then let down. It goes back to small. Is it elastic?

5

Why is a gumboot made of rubber and not cloth?

Show answer

1. 4 cm, because 10 − 6 = 4. 2. Brittle, because it snaps when you bend it. 3. A towel, because it is absorbent and soaks up the drips. 4. Yes, it is elastic, because it goes back to its shape. 5. Rubber is waterproof and bends when you walk; cloth soaks up water.

Summary

Recap

  • Flexible materials bend; thin ones bend most easily.
  • Elastic materials stretch and spring back.
  • Rigid materials are hard to bend; brittle ones snap or shatter.
  • Absorbent materials soak up water; waterproof ones keep it out.
  • To find a stretch, take the first length away from the new length.
  • Pick a material for a job by its properties.
Maths

The maths behind it

Year 3 MathsMeasuring Length, Mass, Capacity and AreaYear 3 MathsAdding and Subtracting up to 1,000
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