# 12.03 Cones, spheres and cylinders

Lesson

## Ideas

Being able to identify the  key features of shapes  can help us in this lesson.

### Examples

#### Example 1

Does a circle have straight or curved edges?

A
Straight
B
Curved
Worked Solution
Create a strategy

A straight edge goes from one vertex to another without any bends. A curved edge has a bend.

Apply the idea

Here is an image of a circle.

The circle has a curved edge that goes all the way around the circle. So the answer is option B.

Idea summary

Edges can be straight or curved.

• A straight edge goes from one vertex to another without any bends.

• A curved edge has a bend.

## Cones, spheres, and cylinders

This video looks at cones, spheres, and cylinders. All these shapes have curved surfaces. Let's see how we can tell which one is which.

### Examples

#### Example 2

Here is a cone.

a

How many faces does it have?

Worked Solution
Create a strategy

Faces are the flat sides of a solid object.

Apply the idea

It has 2 faces: the 1 triangular shape and 1 circle base.

b

How many vertices does it have?

Worked Solution
Create a strategy

In a cone, the vertex is the top point.

Apply the idea

It has 1 vertex.

c

How many edges does it have?

Worked Solution
Create a strategy

An edge is a straight line segment where two faces meet.

Apply the idea

It has 1 curved edge around the circle.

Idea summary
• A curved surface is a surface that is not flat.
• A surface that is flat with a curved edge is still a flat surface.
• Cylinders, cones and spheres all have a curved surface but they do not all have flat surfaces.

### Outcomes

#### MA2-14MG

makes, compares, sketches and names three-dimensional objects, including prisms, pyramids, cylinders, cones and spheres, and describes their features