Identify & name 3D objects
Theory
Identifying and naming 3D objects is a Year 3 maths skill: recognising and naming common solids such as the cube, rectangular prism, sphere, cylinder, cone and pyramid, matching them to everyday objects, and describing their faces, edges and vertices. Curriculum: VC2M3SP01 / AC9M3SP01.
A 3D object is a solid shape that takes up space. Unlike a flat 2D shape, it has length, width and height, so you can hold it and turn it around. A 3D object is also called a solid. Many everyday things are 3D objects: a dice, a ball, a drink can and an ice-cream cone.
We describe a solid by its parts. A face is a flat surface. An edge is a line where two surfaces meet. On a box it is straight; where the flat end of a can meets its curved side, the edge is curved. A vertex is a corner where edges meet, and the word for more than one is vertices. Some solids have a curved surface instead of flat faces, like the round side of a ball or a can.
The six common 3D objects are the cube (all square faces), the rectangular prism (a box shape), the sphere (a ball), the cylinder (a can), the cone (a party hat) and the pyramid (a flat base rising to a point). A prism keeps the same shape all the way along, while a pyramid rises to a single point called the apex. Prisms and pyramids are named after the shape of their ends or base: a triangular prism has two triangle ends, and a square pyramid has a square base.
Naming 3D objects does not need formulas, but this table is handy to pin up. It shows the flat faces, curved surfaces, edges and vertices of each common solid, and everyday objects with each shape are listed under it.
| Object | Flat faces | Curved surfaces | Edges | Vertices |
|---|---|---|---|---|
| Cube | 6 | 0 | 12 | 8 |
| Rectangular prism | 6 | 0 | 12 | 8 |
| Triangular prism | 5 | 0 | 9 | 6 |
| Square pyramid | 5 | 0 | 8 | 5 |
| Triangular pyramid | 4 | 0 | 6 | 4 |
| Cylinder | 2 | 1 | 2 (curved) | 0 |
| Cone | 1 | 1 | 1 (curved) | 1 |
| Sphere | 0 | 1 | 0 | 0 |
Everyday examples: a dice (cube), a cereal box (rectangular prism), a tent (triangular prism), the pyramids of Egypt (square pyramid), a pyramid tea bag (triangular pyramid), a drink can (cylinder), a party hat (cone) and a ball (sphere).
How to name a 3D object
- Flat or curved? Look at the surfaces. If any surface is curved, the object is a sphere, cylinder or cone.
- Look at the faces. Count the flat faces and notice their shapes. All squares means a cube; rectangles means a rectangular prism; triangles rising to a point means a pyramid.
- Prism or pyramid? The same shape all the way along means a prism; a point at the top means a pyramid. Name it after the shape of its ends or base.
- Match the name. Use the shape of the faces and surfaces to choose the object's name, then check it against an everyday object.
It has two flat circular faces and one curved surface, so it is a cylinder. An everyday cylinder is a tin of food or a candle.
| \(\text{faces}\) | \(=\) | \(6\) |
| \(\text{edges}\) | \(=\) | \(12\) |
| \(\text{vertices}\) | \(=\) | \(8\) |
It has \(6\) faces, \(12\) edges and \(8\) vertices, the same as a cube.
Same: both have a curved surface and flat faces shaped like circles, so both can roll.
Different: a cylinder is the same width all the way along and has a flat circle at each end. A cone has a flat circle at one end only and comes to a point (a vertex) at the other.
| \(1\text{ base} + 3\text{ sloping sides}\) | \(=\) | \(4\text{ faces}\) |
It is a triangular pyramid. All \(4\) of its faces are triangles.
Common pitfalls
Frequently asked questions
What is a 3D object?
A 3D object is a solid shape that takes up space and has length, width and height. Cubes, spheres and cylinders are all 3D objects. They are also called solids.
What is the difference between a cube and a rectangular prism?
Both have 6 flat faces, 12 edges and 8 vertices. On a cube every face is a square of the same size. On a rectangular prism the faces are rectangles, so it can be longer in one direction, like a cereal box.
How do you name a prism or a pyramid?
Look at its ends or its base. A prism is named after the shape of its two matching ends, like a triangular prism. A pyramid is named after the shape of its base, like a square pyramid.
What everyday objects are cylinders?
A tin of food, a roll of paper towel, a candle and a water tank are all cylinders. Each has a flat circle at both ends and one curved surface.
What is the difference between a prism and a pyramid?
A prism has two identical end faces and stays the same shape all the way along. A pyramid has one flat base and rises to a single point called the apex.
What is a face, an edge and a vertex?
A face is a flat surface of a solid. An edge is the line where two faces meet. A vertex is a corner where edges meet. Vertices is the word for more than one vertex.