Symmetry: mirrors and turns
Hold a mirror across tiles, a kite and the flag of Nepal, and turn them about their centre to find their lines and order of symmetry.
Core concept
In short: Fold and turn shapes to find their lines of symmetry.
A line of symmetry reflects a shape onto itself; rotational symmetry turns it onto itself before a full turn
Topic: Symmetry
Fold a square tile along its diagonal and the two halves match: the fold line is a line of symmetry: When one half of a shape is a mirror image of the other half. All key words. A mirror on that line shows the same shape. A shape has rotational symmetry if, when turned about its centre by less than a full turn, it lands exactly on itself; the number of times this happens in one full turn is its order. Some shapes have both kinds of symmetry, some only one, and some, like the flag of Nepal, have neither.
What you will learn
- Find the lines of symmetry of a shape.
- Find the order of rotational symmetry of a shape.
- Recognise shapes with rotational symmetry but no line of symmetry.
Before you start
- Names of common shapes; angles of 90° and 180°.
Materials
- Paper shapes and a small mirror
Equipment
- Tracing paper and a pin to turn it
Procedure
- Tap the shape card to choose a shape.
- Tap the mirror chip to hold a mirror along a line; a green outline means it matches.
- Tap the turn chip to turn a copy about the centre.
- Record a shape matching a diagonal mirror, a shape that matches only after a half turn, a hexagon turned by 60°, and the flag of Nepal in a mirror.
How this simulation is simplified
- Mirrors and turns go through the centre of the shape.