Grade by Grade
E. Spatial Sense · 3D Objects, Directions and Measurement

Structures: Putting 3D Objects Together

E1.2 A1About 35 minutes
Learning goals
  • I can build a structure by putting 3D objects together.
  • I can take a structure apart and name the 3D objects in it.
  • I can name the 2D shapes I see on a structure.
  • I can keep trying and change my plan when my structure falls down.

Words to know

structure
Something that is built from parts, like a house, a bridge, a tower or a snow fort.
compose
To put objects or shapes together to make something new.
decompose
To take something apart (or imagine taking it apart) to see the pieces it is made from.
2D shape
A flat shape, like a square, rectangle, triangle or circle. The faces of 3D objects are 2D shapes.
3D object
A solid object like a cube, prism, pyramid, cylinder or cone.

Let's start with a look around

Look out your window. You might see houses, a garage, a bridge, a playground or a snow fort. These are all structures: things that people build out of parts.

If you look closely, structures are made of the 3D objects you know: prisms, pyramids, cylinders and cones. And on their faces, you can find 2D shapes: rectangles, squares, triangles and circles.

A green steel truss bridge crossing a calm river with trees on both banks.
This bridge is a structure built from parts. Look for the triangles on its sides and the rectangular prism shape of the whole bridge. AI-generated image

Compose and decompose

  • To compose means to put together. When you stack blocks to make a castle, you compose a structure.
  • To decompose means to take apart. You can really take the blocks apart, or you can take the structure apart in your mind and name each piece.

When you describe a structure, name the 3D objects it is made of, and the 2D shapes you can see on it.

roof: triangular prismhouse: rectangular prismdoor: rectanglewindows: squaresend of roof: triangle
A house made of a rectangular prism with a triangular prism roof. On its faces you can see a rectangle door, square windows and a triangle at the end of the roof.
Worked example

Example 1: Decompose a house

Look at the house picture. What 3D objects is it made of? What 2D shapes can you see?

  1. The main part of the house is like a box: a rectangular prism.
  2. The roof has a triangle at each end and long rectangle faces on the slopes: a triangular prism.
  3. Now look for flat shapes on the faces: the door is a rectangle, the windows are squares, and the end of the roof is a triangle.

3D objects: a rectangular prism and a triangular prism. 2D shapes: rectangles, squares and triangles.

towercylindercone+
A tower made of a cylinder with a cone on top. Decomposed, it is one cylinder and one cone.
Worked example

Example 2: Compose a tower

Jaden has a cube, a cylinder and a cone. He wants to stack all three into one tall tower. In what order should he stack them?

  1. The cone comes to a point. Nothing can sit on top of a point, so the cone must go at the top.
  2. The cube and the cylinder both have flat faces on the top and bottom, so they can stack.
  3. A cube on the bottom is very steady, then the cylinder stands on its circle face, then the cone sits on the cylinder's top circle.

Bottom to top: cube, cylinder, cone. (Cylinder, cube, cone also works.) The cone must be on top.

An Inuit structure: the inuksuk

An inuksuk is a structure made of stones. Inuit have built inuksuit (that is the word for more than one) on the land for a very long time. Inuksuit can help people find their way and can share messages with travellers. An inuksuk appears on the flag of Nunavut.

Builders choose and balance each stone carefully. Many of the stones are shaped a bit like rectangular prisms, and from the front you can see rectangle shapes. An inuksuk built in the shape of a person, like the one in the drawing below, is called an inunnguaq.

A simple drawing of an inuksuk seen from the front. Each stone looks like a rectangle from the front, a bit like a rectangular prism in real life.
Worked example

Example 3: A winter structure

A snowman has 3 snowballs, a carrot nose and a hat shaped like a can. Decompose it into 3D objects.

  1. Snowballs are round in every direction, like a ball. A ball is called a sphere.
  2. A carrot is wide at one end and comes to a point at the other: like a cone.
  3. The hat has a flat circle top and bottom and a curved side: a cylinder.

The snowman is made of 3 spheres, a cone and a cylinder.

When your structure falls down

Every builder has things fall down! That's how builders learn. If your tower falls, don't give up. Ask:

  • Did I put a big flat face at the bottom?
  • Is a curved surface rolling?
  • Is something with a point trying to hold something up?

Change one thing and try again. Taking a deep breath before you try again helps too.

Just for fun

Why does the cone always go on the top of the tower?

Because it likes to make a point!

Hands-on activity

Recycling bin builders

You need: clean boxes, cans with smooth edges, paper towel tubes, a paper cup and some tape.

Grown-up note: check that cans have no sharp edges.

  1. Build a structure: a castle, a bridge, a rocket or a house.
  2. Draw your structure or ask a grown-up to take a photo.
  3. Make a list of every 3D object you used: "2 rectangular prisms, 1 cylinder, 1 cone ..."
  4. Look at the outside. List the 2D shapes you can see.
  5. Take your structure apart. Give your list to someone in your family. Can they build something like it using only your list?

Math talk: "Which objects were the best for the bottom? Why?"

Your turn

1

What does decompose mean?

2

A rocket is made of a cylinder with a cone on top. Which object is on top? Why does it make sense?

3

Name the 2D shape you see on the end of a triangular prism roof.

4

A tall apartment building looks like a big box. Which 3D object is it like?

5

You stack 2 cubes. What 3D object does the stack look like?

6

Name a 2D shape you can see on the top of a cylinder.

7

What can you do if your block tower keeps falling over?

More practice: warm-up

1

What does compose mean?

2

Is a house a structure?

3

What 3D object is a tissue box like?

4

What 2D shape is a window on a house often like?

5

Can a cone hold up a cube on its tip?

More practice: on your own

1

A birdhouse has a box shape with a roof that slopes down on two sides. Decompose it into 3D objects.

2

A castle tower is a cylinder with a cone on top. When you look at it from the side, what 2D shapes do you see?

3

Mia used 4 cubes in a row to make a train. Then she added a cylinder on top of the first cube for a chimney. How many 3D objects are in her train? Name them.

4

Why do many builders put a rectangular prism at the bottom of a structure, not a cylinder lying on its side?

5

A playground slide has a ladder, a flat platform and a slide. Name a 3D object the platform could be like, and a 2D shape you could see on it.

Challenge

1

Design a structure using exactly 1 cube, 2 cylinders and 1 square-based pyramid. Describe where each piece goes.

2

A tower is made of 3 cubes stacked up. How many cube faces are hidden (touching another cube or the floor)?

3

A square-based pyramid sits on top of a cube whose faces are the same size as the pyramid's base. How many faces does the whole structure have that are not covered by the other object? (Count the bottom face too.)

Check your understanding

Quiz

1.

What does compose mean?

2.

A rocket is a cylinder with a cone on top. If you decompose it, what do you get?

3.

Which 3D object can not have anything stacked on top of it?

4.

What 2D shape do you see at the end of a triangular prism roof?

5.

Which object makes the steadiest bottom for a tower?

6.

An inuksuk is ...

For parents and teachers

Big idea: Children compose and decompose structures and identify the 2D shapes and 3D objects within them (Ontario E1.2). Building also gives a natural chance to practise perseverance and managing frustration (strand A1).

Common difficulties:

  • Mixing 2D and 3D names (calling a box a "rectangle"). Help your child say "It's a rectangular prism, and its faces are rectangles."
  • Seeing only the front. Encourage walking around a structure or turning a model to see all its parts.
  • Frustration when things fall. Name the feeling, take a breath, and change one thing at a time.

About the inuksuk: Inuksuit are important structures in Inuit culture and are built with great skill and purpose. Please treat them with respect: real inuksuit on the land should never be knocked down or moved.

Safety: Check cans for sharp edges before building.

How to help: On a walk, play "I spy a structure": name a building and the 3D objects it's made of.