Grade by Grade
E. Spatial Sense · Shapes, Position and Measurement

Building 3D Objects and Finding 2D Faces

E1.2About 30 minutes
Learning goals
  • I can build 3D objects and structures using blocks, boxes and other things.
  • I can find flat 2D shapes on the faces of 3D objects.
  • I can find 2D shapes in buildings and structures around me.

Words to know

face
A flat surface on a 3D object. A cube has 6 faces.
edge
The line where two faces meet.
vertex
A corner where edges meet.
structure
Something built from parts, like a tower, a house, a bridge or a snow fort.
print (trace)
The flat shape you get when you press or trace around one face of an object.

Have you ever built a tower with blocks or a snow fort in winter? Builders use 3D objects like cubes and prisms. And hiding on every 3D object are flat 2D shapes! Let us find them.

Faces are flat shapes

A face is a flat part of a 3D object. If you dip a face in paint and press it on paper, you get a flat 2D shape. This is called a print.

cylindercircle printcubesquare print
A cylinder makes a circle print. A cube makes a square print.
3D objectIts faces are...How many faces?
cubeall squares6
rectangular prism (box)rectangles (sometimes some are squares)6
cylinder2 circles (plus one curved surface)2 flat faces
cone1 circle (plus a curved surface and a point)1 flat face
square-based pyramid1 square and 4 triangles5
sphereno flat faces at all0
Faces of common 3D objects.

Remember

A curved surface is not a face because it is not flat. That is why a sphere has no faces and why it rolls in every direction.

Worked example

Counting the faces of a cube

How many faces does a toy block (a cube) have, and what shape are they?

  1. Hold the cube. Put a small sticker or a piece of tape on the face on top.
  2. Turn the cube and touch each new face, putting a sticker on each one: top, bottom, front, back, left side, right side.
  3. Count the stickers: 1, 2, 3, 4, 5, 6.
  4. Look at one face. It has 4 straight sides that are all the same length, so it is a square.

A cube has 6 faces, and every face is a square.

Worked example

Finding 2D shapes in a structure

Look at a house. What 2D shapes can you find?

  1. The door is tall with 2 long sides and 2 short sides: a rectangle.
  2. Many windows are squares or rectangles.
  3. The roof, seen from the front, often makes a triangle.
  4. Some houses have a round window: a circle.

A house can have rectangles, squares, triangles and circles hiding in it.

trianglesquarecirclerectanglerectangle(window)(roof)(round window)(door)(wall)
2D shapes hiding in a house: the roof is a triangle, the windows are squares and a circle, and the door and the wall are rectangles.

Building with 3D objects

When you build, think about which objects work best:

  • Cubes and rectangular prisms stack well because their faces are flat.
  • Cylinders stack if you stand them on their flat circle faces. They make good towers and pillars.
  • Spheres roll away, so they are tricky to build with!
  • Cones and pyramids have a point, so they are great for the very top of a tower or a castle roof.
Worked example

Plan a tower

You want to build the tallest tower you can. You have 3 cubes, 1 sphere and 1 cone. Which order should you use?

  1. Cubes have flat faces on top and bottom, so stack the 3 cubes first.
  2. The cone has a flat circle face on the bottom and a point on top. It can sit on top of the cubes.
  3. The sphere would roll off a cone point, so leave it off (or put it at the very bottom held in place, but it will wobble).

Stack the 3 cubes, then put the cone on top like a roof. The sphere does not stack well.

Just for fun

What if you built a house out of spheres? Every time you leaned on a wall, it would roll away! That is why builders love cubes and prisms with flat faces.

Hands-on activity

Box city and shape prints

  1. Collect empty boxes, cans, toilet paper rolls and yogurt cups (recycling bins are great for this).
  2. Build a structure: a house, a castle, a hockey arena or a CN Tower. Tape it together if you like.
  3. Name each 3D object you used.
  4. Shape prints: with a grown-up, dip faces of the objects into a little paint (or trace around them with a crayon) on paper. Label each print: circle, square, rectangle or triangle.
  5. Walk around your home or neighbourhood and list 2D shapes you see in buildings: doors, windows, roofs, signs (a stop sign is an octagon, with 8 sides!).

Your turn!

1

What shape is each face of a cube?

2

If you trace the bottom of a soup can, what shape do you get?

3

How many flat faces does a cylinder have?

4

What 2D shapes are the faces of a cereal box?

5

Why is a sphere hard to build with?

6

Look at a window in your home. What 2D shape is it?

7

A square-based pyramid has a square on the bottom. What shape are its other faces?

More practice: warm-up

1

Fill in the blank: a flat part of a 3D object is called a ___.

2

True or false: a sphere has flat faces.

3

You dip the flat bottom of a cone in paint and press it on paper. What shape is the print?

4

How many faces does a cube have?

5

Which are better for stacking: cubes or spheres?

More practice: on your own

1

How many flat faces do a cylinder and a cone have all together?

2

Look at a juice box. What 2D shapes are its faces? What is the whole 3D object called?

3

Sam says, "A tissue box is a rectangle." Help Sam say it the right way.

4

A stop sign is an octagon. How many sides does it have?

5

Which 3D object can make a triangle print: a cube, a cylinder, or a square-based pyramid?

Challenge

1

Find the mistake! Jay says, "A cylinder has 3 faces: 2 circles and the curved part." What is wrong?

2

You have 2 cubes, 1 cylinder and 1 cone. Plan a tower that uses all four and will not fall over. Explain your order.

3

Mystery object: I have 2 flat faces that are circles, and I can roll. What am I? Name another 3D object that has only 1 circle face.

Check your understanding

Quiz

1.

What shape is the print of a cube?

2.

Which object has no flat faces?

3.

Which 3D object would be best at the very top of a castle tower, like a pointy roof?

4.

What 2D shape do you usually see in a door?

5.

How many faces does a cube have?

6.

Which object has faces that are triangles?

For parents and teachers

What your child is learning: building with 3D objects and recognizing that the flat faces of those objects are 2D shapes. They also look for 2D shapes in real structures (Ontario Grade 1, E1.2).

Common mistakes:

  • Calling a whole object by its face name ("this box is a rectangle"). Say: "Its faces are rectangles. The whole box is a rectangular prism."
  • Counting the curved surface of a cylinder or cone as a face. Explain that a face must be flat.
  • Losing track while counting faces. Using stickers or tape on each face you count really helps.

How to help: let your child build freely with blocks, LEGO, boxes or even snow. Ask: "Why did you put that one on the bottom?", "Which shapes stack best?", "What flat shapes can you see in your building?" On walks, play "I spy a shape" with signs, windows and doors. Encourage your child to keep trying when a tower falls, and to talk about what to change next time.