Page 136 - ICSE Math 5

Rotational symmetry

Rotation means turning or rotating a figure around its centre or a fixed point. The fixed point
around which a figure is rotated is called the centre of rotation. It can be rotated either clockwise
or anticlockwise.

Look at the figures of pinwheel shown below to understand the clockwise and anticlockwise
rotation around a fixed point.

Centre of Centre of
rotation rotation

Clockwise rotation Anticlockwise rotation

A two-dimensional figure or shape is said to have rotational symmetry when it looks exactly the
same at least once after a rotation around a fixed point.
Quarter turn

A quarter turn refers to a rotation of 90°.
Look at the given shape.

Put a dot on one end of the shape and give it a quarter turn.

With the help of the dot, we can see that the shape looks different after a 90°
quarter turn and forms an angle of 90°.

Some shapes that look the same even after a quarter turn are shown below.

These show rotational symmetry since they look exactly the same after a quarter turn.

126