Grade by Grade
D. Structures and Mechanisms · Materials, Objects, and Everyday Structures

Choosing the Right Material for the Job

D2.4 D2.5 D2.6 A1.2 A1.4 A1.5About 35 minutes
Learning goals
  • I can describe properties of materials, like hard, soft, bendy, stiff, waterproof and see-through.
  • I can tell the purpose (the job) of an everyday object.
  • I can explain why a material is a good choice for an object's job.
  • I can do a fair test to find out which material soaks up water best.

Words to know

property
Something we can observe about a material, like hard, soft, bendy or waterproof.
purpose
The job an object is made to do. The purpose of a cup is to hold a drink.
waterproof
Does not let water through. Rubber boots are waterproof.
absorbent
Soaks up water. A towel is absorbent.
flexible
Bends easily without breaking.
transparent
See-through. You can see clearly through a window.
fair test
A test where we change only one thing and keep everything else the same.

A silly question

Would you like an umbrella made of paper? What would happen in the rain?

The paper would get soggy and rip, and you would get wet! That is why umbrellas are made of materials that keep water out.

Every object has a job to do. People choose materials that are good at that job.

An open red umbrella lying on a wet sidewalk in the rain, covered in raindrops.
The raindrops sit on top of this umbrella instead of soaking through. Its material is waterproof, so it is just right for the job. AI-generated image
paper umbrellaplastic umbrellasoggy and torn: you get wet!waterproof: you stay dry!
An umbrella's job is to keep you dry, so it needs a waterproof material. Paper soaks up water and tears. Plastic keeps the rain out.

Purpose means the job

The purpose of an object is the job it does.

  • The purpose of a cup is to hold a drink.
  • The purpose of a mitten is to keep your hand warm.
  • The purpose of a window is to let light in and keep the wind and snow out.

Properties of materials

A property is something we can observe about a material. Here are some important ones.

PropertyWhat it meansExample
hard / softpushes back / squishesa wooden block is hard; a pillow is soft
stiff / flexibledoes not bend / bends easilya ruler is stiff; a rubber band is flexible
waterproof / absorbentkeeps water out / soaks up waterrubber boots are waterproof; a towel is absorbent
transparent / not see-throughyou can see through it / you can'tglass is transparent; wood is not
strong / weakholds weight without breaking / breaks or tears easilymetal is strong; tissue paper is weak
warm (keeps heat in)helps keep heat inwool keeps you warm
Properties help us choose the right material
☔🥾🪟🧣🧽
Umbrella (waterproof), boot (waterproof), window (transparent), scarf (keeps you warm), sponge (absorbent)

Matching the material to the job

To choose a material, ask: What is the job? Then ask: Which property helps do that job?

A window needs to let you see outside, so it must be transparent. Glass is transparent, so we use glass.

A towel needs to dry you, so it must be absorbent. Cotton fabric is absorbent, so we use cotton.

Worked example

Let's choose a material for rain boots

Which material is best for rain boots: paper, rubber or wool?

  1. Purpose: Rain boots must keep your feet dry in puddles.
  2. Property we need: The material must be waterproof.
  3. Paper soaks up water and tears. Not good!
  4. Wool soaks up water too. Not good for puddles!
  5. Rubber keeps water out. It is also flexible, so you can walk.

Rubber is best because it is waterproof and flexible.

Worked example

Let's do a fair test: which material soaks up water best?

We will test a paper towel, a piece of plastic bag, and a cotton washcloth (or sock).

  1. Question: Which material soaks up the most water?
  2. Predict: I think the washcloth will soak up the most, because towels dry me after a bath.
  3. Make it fair: Cut each material to about the same size. Pour the same amount of water (1 spoonful) on a plate for each one. Lay each material on its water for the same time (count to 20).
  4. Observe: Lift each one. The plastic is still dry on top and the water is still on the plate. The paper towel and washcloth soaked up the water.
  5. Record what we saw in a chart.

The paper towel and the washcloth are absorbent. The plastic is waterproof. The washcloth did soak up water, as we predicted. (Your results may be a little different. That's okay! Scientists share what they really saw.)

MaterialDid it soak up the water?Absorbent or waterproof?
paper towelyesabsorbent
plastic bagnowaterproof
cotton washclothyesabsorbent
Our results chart

A fair test

In a fair test we only change one thing (here, the material). We keep the amount of water, the size and the time the same. Then we know the material made the difference.

Just for fun

Riddle: What gets wetter the more it dries?

A towel! It is absorbent, so it soaks up the water from you.

Hands-on activity

Soak-it-up test at home

You need: a plate or tray, a spoon, water, and small squares (about the size of your hand) of: paper towel, aluminum foil, a cotton sock or washcloth, and a piece of a plastic bag.

  1. Predict: Which one will soak up the most water? Which will keep the water out?
  2. Put 1 spoonful of water on the plate for each material, spread apart.
  3. Lay each square on a puddle. Count to 20 together.
  4. Lift each one. Which puddles are gone? Which material is wet?
  5. Draw a chart: material, soaked it up? yes or no.
  6. Tell a grown-up what you found out. Was your prediction right?

Safety: Wipe up spills right away so no one slips. Ask a grown-up to cut the squares.

Your turn

1

What is the purpose of a coat?

2

Why are windows made of glass?

3

Is a sponge absorbent or waterproof?

4

Would you make a hockey net frame from metal or from paper? Why?

5

Name something that is flexible.

6

Why is a towel made of cotton fabric and not plastic?

7

In a fair test, what do we change?

More practice: warm-up

1

Is a rock hard or soft?

2

Is a pillow hard or soft?

3

What is the purpose of a spoon?

4

Can you see through a clear plastic water bottle?

5

Do rubber boots let water in?

More practice: on your own

1

Choose the best material for a toboggan: paper, plastic or fabric. Explain.

2

Why are mittens made of wool or fleece?

3

Why is a frying pan made of metal and not plastic?

4

A tent must keep campers dry. What property should the tent material have?

5

Sam tested a sponge with 1 spoonful of water and a paper towel with 5 spoonfuls. Was it a fair test?

Challenge

1

A drinking straw is made of plastic, paper or metal. Pick one and give one good property and one problem.

2

Why is a hockey helmet hard on the outside and soft on the inside?

3

Design a lunch bag. Name a material and say how its properties help.

Check your understanding

Quiz

1.

What does waterproof mean?

2.

What is the purpose of a window?

3.

Which material is best for a towel?

4.

Which is transparent?

5.

Why is a bike tire made of rubber?

6.

To make a soaking test fair, we should...

For parents and teachers

Big idea: Objects have a purpose (job), and materials are chosen because their properties help the object do that job (Ontario expectations D2.5 and D2.6).

How to help: Ask "Why do you think this is made of ___?" about everyday things: a metal pot, a glass window, a rubber boot, a wool toque. Good answers name a property: strong, waterproof, see-through, soft, flexible.

About the experiment: This is your child's first fair test (Strand A, scientific experimentation). Help them predict, keep things the same, observe and say what happened. Results may differ from predictions; praise honest reporting.

Common difficulties:

  • Describing the object instead of the material ("the boot is a boot"). Prompt: "What is the boot made of? What is that material good at?"
  • Mixing up absorbent and waterproof. Link them to a towel (absorbent) and rubber boots (waterproof).
  • Changing two things in a test. Ask, "What did we keep the same?"