Grade by Grade
D. Structures and Mechanisms · Strong and Stable Structures

Choosing Materials for Strong and Stable Structures

D2.5 D2.3 A3.3 A1.2 A1.4About 40 minutes
Learning goals
  • I can name properties of materials that builders think about, like strength, stiffness, weight, waterproofness, how long it lasts and cost.
  • I can explain why a material is a good or poor choice for a structure.
  • I can describe how First Nations, Métis and Inuit builders have chosen materials from the land for their structures.
  • I can test materials to compare their properties.

Words to know

material
What something is made of, like wood, steel, concrete, plastic or snow.
property
A feature of a material that tells what it is like, like hard, bendy, heavy or waterproof.
stiff
Hard to bend. The opposite of flexible.
flexible
Able to bend without breaking.
durable
Lasts a long time without wearing out, rotting or rusting.
waterproof
Does not let water through.
insulator
A material that slows heat from moving through it. It helps keep a home warm in winter.

The three little pigs had it right!

In the old story, one pig builds with straw, one with sticks and one with bricks. The brick house stands up to the wolf. That story is about choosing materials!

But real builders think about much more than strength. A brick house would be a terrible choice for a canoe! The best material depends on the job.

Remember from Grade 1

In Grade 1 you learned that materials have properties, like hard, soft, bendy, waterproof or see-through, and that people choose materials that fit an object's job. Now we use those ideas to choose materials for structures.

Properties builders think about

  • Strength: Can it hold a heavy load without breaking?
  • Stiffness or flexibility: Should it stay stiff (a floor) or bend a little (a fishing rod, a tree in the wind)?
  • Weight: Heavy materials add to the dead load. Light materials are easier to carry and float better.
  • Waterproof: Does it keep out rain, snow and water?
  • Durability: Will it last? Does it rot, rust or crack in the cold?
  • Insulation: Does it help keep heat in during winter?
  • Cost and how easy it is to get: Is it close by? Is it too expensive?
  • Environment: Can it be reused or recycled? Does getting it harm the land?
  • Safety: Is it safe to touch and live with?
A building site with a stack of wooden boards, a pallet of red bricks, a pallet of grey concrete blocks and steel beams.
Wood, brick, concrete and steel each have different properties. Builders choose the one that best fits each part of the job. AI-generated image
MaterialHelpful propertiesWatch out forUsed for
woodstrong for its weight, easy to cut, renewable (trees can be replanted)can rot when wet; can burnhouse frames, decks, furniture
steelvery strong, stiff, lasts a long timeheavy; can rust if not protectedbridges, tall buildings, cranes
concretevery strong when squeezed, waterproof, does not burnheavy; cracks when stretched (steel rods help)foundations, sidewalks, dams
brick and stonestrong when squeezed, last a very long timeheavy; hard to shapewalls, chimneys, old bridges
glasslets light through, waterproofbreaks easily when hitwindows
plasticlight, waterproof, can be shapedsome kinds crack in cold or sunlight; many are hard to recyclepipes, playground slides
Some common building materials and their properties
Worked example

Let's choose a material

You are building a bus shelter in your town. It must keep people dry, let them see the bus coming, and last for many winters. Which materials would you choose for the frame and the walls?

  1. Frame: it must be strong and durable outdoors. Steel (painted so it will not rust) or aluminum is a good choice. Wood could rot.
  2. Walls: people must see the bus, so the walls should let light through. Glass or clear plastic works.
  3. Roof: it must be waterproof and hold snow. A strong, waterproof roof of metal, or thick clear plastic on the strong frame.
  4. Base: a concrete pad anchors it so wind cannot move it.

A metal frame, clear walls, a waterproof roof and a concrete base. Each material was chosen for a property that fits its job.

ROOFwaterproof, holds snowFRAMEpainted steel or aluminumWALLSglass or clear plasticBASEconcrete pad (anchor)
Each part of the bus shelter uses a material with the right property for its job.

Learning from First Nations, Métis and Inuit builders

For thousands of years, First Nations, Métis and Inuit builders have chosen materials from the land very carefully, using deep knowledge of each material's properties. Here are some examples:

  • Iglu (snow house), Inuit: Builders cut blocks of firm, wind-packed snow with a snow knife and stack them in a spiral to make a dome. Snow is everywhere in the Arctic winter, it is light to lift, and the air trapped in snow makes it a good insulator, so the inside stays much warmer than the outside. The dome shape is strong and sheds wind.
  • Qajaq (kayak), Inuit: A light frame of driftwood or bone covered with sealskin. The skin is waterproof and the frame is light and flexible. People all over the world now use kayaks.
  • Wigwam (waaginogaan), Anishinaabe: Young, flexible trees (saplings) are bent into a dome frame and tied together, then covered with birchbark or woven mats. Birchbark is light and sheds water.
  • Longhouse, Haudenosaunee: A long frame of wooden poles bent into an arched roof, covered with large sheets of elm bark. Several families could live in one longhouse.
  • Birchbark canoe, many First Nations including the Anishinaabe: A frame of cedar covered with birchbark, sewn with spruce root and sealed with tree gum. It is light enough to carry between lakes and easy to repair.
  • Log houses, Métis: Many Métis families at Red River (in what is now Manitoba) built log houses, often in a style called Red River frame, with short logs fitted into grooves in upright posts.
cold wind slidesover the domeBLOCKS of wind-packedsnow, stacked in a spiralDOME SHAPEstrong and sheds windAIR TRAPPED IN SNOWinsulates: inside staysmuch warmer than outside
An Inuit iglu: blocks of wind-packed snow stacked in a spiral make a strong dome. Air trapped in the snow keeps the heat in.

Respect and learning

These are not just things from the past. First Nations, Métis and Inuit people still build and use many of these structures today, and builders and engineers keep learning from them. When we learn about them, we use their correct names and the names of the Nations who made them.

Worked example

Let's explain a material choice

Why was birchbark a good material for a canoe?

  1. A canoe must float and keep water out. Birchbark sheds water, and sealing the seams with tree gum makes the canoe watertight.
  2. A canoe must be light to carry between lakes. Birchbark is thin and light.
  3. Birch trees grow in many forests, so the bark was available nearby.
  4. A canoe must be repairable on a trip. Bark, root and gum could be found in the forest to patch it.

Birchbark is light, sheds water, was easy to find, and could be repaired: all properties that fit a canoe's job.

Just for fun

The third little pig would make a great engineer. She picked her material for strength before the wolf showed up to test it!

Hands-on activity

Material test station

You need: small squares (about 10 cm) of paper, cardboard, aluminum foil, a plastic bag, and cloth; a spoon; water; two stacks of books; and a few coins.

  1. Waterproof test: put a spoonful of water on each square over a plate. After 1 minute, lift it. Did water soak through?
  2. Strength test: lay each square across a small gap (5 cm) between two stacks of books. Add coins to the middle one at a time. How many does each hold before it sags to the table?
  3. Flexibility test: gently bend each one. Does it bend and spring back, stay bent, or crack?
  4. Make a table: material, waterproof (yes/no), coins held, flexible (yes/no).
  5. Decide: which would be best for a tent roof? A bridge deck? Explain using properties.

What to look for: foil and plastic are waterproof; cardboard is the strongest of these; cloth and plastic are flexible. A tent roof needs waterproof and flexible (plastic); a bridge deck needs strong and stiff (cardboard of these). Safety: wipe up spills; keep coins and plastic bags away from little children.

Your turn

1

What is a property of a material?

2

Name three properties builders think about.

3

Why are windows made of glass?

4

Why do builders protect steel with paint?

5

What material did Inuit builders use for an iglu?

6

Why is snow a good material for an iglu?

7

Why would brick be a poor choice for a canoe?

More practice: warm-up

1

Does a material that lasts a long time have good durability or poor durability?

2

Is concrete strong when it is squeezed?

3

Which material sheds water and was used to cover wigwams and canoes?

4

Is plastic heavy or light?

5

Name one material that can rot when it gets wet.

More practice: on your own

1

A builder wants a deck that will last for years outdoors in rain and snow. What property is most important? Name a good material.

2

Why are tall buildings and long bridges made with steel?

3

Why did Anishinaabe builders use young, flexible trees (saplings) for the frame of a wigwam?

4

In the material test, foil held water but cardboard held the most coins. Which would you pick for a model bridge deck, and why?

5

Why might a builder choose a material from close by instead of one from far away?

Challenge

1

A playground is being built in a park near a lake. Choose materials for the slide, the climbing frame and the ground underneath. Give a property for each.

2

Concrete is strong when squeezed but cracks when stretched. Steel is strong when stretched. Why do builders put steel rods inside concrete for a bridge?

3

Compare an iglu and a wood-frame house. Name one way they are alike and one way they are different, using properties of materials.

Check your understanding

Quiz

1.

A property of a material is...

2.

Which material would be best for a window?

3.

A durable material...

4.

Why is snow a good material for an iglu?

5.

Birchbark was a good choice for canoes because it is...

6.

Which is a poor choice for the walls of a house in a snowy place?

For parents and teachers

Big idea: Builders consider properties of materials such as strength, stiffness or flexibility, weight, waterproofness, durability, insulation, cost, availability, environmental impact and safety (D2.5, D2.3). Learning how First Nations, Métis and Inuit builders chose materials from the land, such as snow for iglus, birchbark for canoes and wigwams, elm bark for longhouses and log construction at Red River, honours their knowledge and contributions (A3.3). The material test station is a hands-on investigation (A1.2, A1.4).

How to help: Walk around your home and ask, "Why is this made of that?" (a metal pot, a wooden spoon, a rubber boot, a glass window). Ask your child to name the property that makes it a good choice.

Common difficulties:

  • Thinking one material is "best" for everything. The best material depends on the job.
  • Naming only strength. Encourage other properties: weight, waterproof, durable, cost.
  • Describing Indigenous structures only in the past tense. Many are still built and used today; use specific Nation names (Inuit, Anishinaabe, Haudenosaunee, Métis) rather than one general label.

Safety: wipe up spills; keep coins and plastic bags away from young children.