3D shapes
Naming 3D shapes
This unit introduces prisms and pyramids. You compare them to see what is the same and what is different, and you name and describe 3D shapes using their faces, edges and vertices.
Faces, edges and vertices
Every 3D shape can be described by its parts: • A face is a flat surface of the shape. • An edge is a straight line where two faces meet. • A vertex is a corner where edges meet (more than one are called vertices). Example: a cube has 6 faces, 12 edges and 8 vertices.
Prisms
A prism has two ends that are exactly the same shape and size. The faces are flat, and the sides that join the two ends are rectangles. A triangular prism has two triangle ends. A cube and a cuboid are prisms too.
Pyramids
A pyramid has one base and its side faces are triangles that rise to meet at a single point called the apex. A square-based pyramid has a square base and 4 triangular faces. A triangular pyramid has 4 triangular faces in all.
Shapes with curved surfaces
Some shapes are not prisms or pyramids because they have curved surfaces: • A sphere is round all over — no faces, edges or vertices. • A cylinder has 2 flat circular faces and a curved surface. • A cone has 1 flat circular face, a curved surface and 1 vertex.
Worked examples
Counting the parts of a cube
- Count the flat surfaces (faces): top, bottom and 4 sides = 6.
- Count the straight lines where faces meet (edges) = 12.
- Count the corners (vertices) = 8.
Answer: A cube has 6 faces, 12 edges and 8 vertices.
Is it a prism?
- Check the ends: are they the same shape and size?
- Check the faces: are they all flat, with rectangles joining the ends?
- A triangular prism has two matching triangle ends and flat faces.
Answer: Yes — a triangular prism is a prism.
Is it a pyramid?
- Look for one base and side faces that are triangles.
- Check that the triangles rise to meet at a single point (the apex).
- A square-based pyramid has a square base and 4 triangular faces.
Answer: Yes — a square-based pyramid is a pyramid.
Where you see this in real life
- A dice or a box is a cube or a cuboid.
- A tin of food is a cylinder and a ball is a sphere.
- An ice-cream cone is a cone, and a tent can be a triangular prism.
Key words
- Face
- A flat surface of a 3D shape.
- Edge
- A straight line where two faces meet.
- Vertex
- A corner where edges meet (more than one are vertices).
- Prism
- A 3D shape with two ends the same shape and size, joined by flat rectangular faces.
- Pyramid
- A 3D shape with a base and triangular faces that meet at a point (the apex).
- Apex
- The single point at the top of a pyramid or cone where the faces meet.