How_To_Be_Good_At_Math

262 GEOMETRY •^ ROTATION

Rotation

Rotation is a kind of transformation, in which an object or shape

turns around a point called the centre of rotation. The amount we

rotate the shape is called the angle of rotation.

When we rotate A around

the centre of its longest

side, half of the new triangle

overlaps the old one.

First, let’s rotate triangle A

around one of its vertices to

make a new triangle. We call the

new triangle A’.

When A rotates around

its centre, a different part

of the new triangle overlaps

the middle of the old one.

Centre of rotation

The centre of rotation is a fixed point, which means it doesn’t move. Let’s look at what

happens when we rotate the same shape clockwise around different centres of rotation.

A

A’

A

Centre of

rotation

Centre of

rotation

Centre of

rotation

Angle of

rotation

is 90°

Angle of rotation is 180°

Original

position

of sail

Angle of

rotation is

270°

Centre of

rotation

A

A’

A’

This time, the sail

has rotated 180°,

or two right angles.

This windmill

sail has rotated

through 90° (a right

angle).

Now the sail has

rotated through

270°, or three right

angles in total.

Angle of rotation

The angle of rotation

is the distance that

something rotates

around a point,

measured in

degrees. Let’s see

what happens to

this windmill sail

when we rotate it by

different amounts.

262_263_Rotation.indd 262 11/03/2016 16:24