Symmetry in a circular motion

Defining Rotational Symmetry

Rotational Symmetry happens when a shape or a design can be turned around its centre of rotation so that it actually fits onto its outline more than once in a complete turn

Now, a centre of rotation is the point around which you turn the object or the designUsually, the centre of rotation is the exact centre of

the design.However, a centre of rotation can also be “off center”

Don’t forget: a design can have BOTH line symmetry and rotation symmetry.

Examples:The centre of rotation is noted with a red dot

in the following designs or shapes:

Examples of “off centre” rotationsThese designs have a centre of rotation that

is considered “off centre”

Order of RotationThe order of rotation is

the number of times which a shape or design fits into itself in one, complete turn of 360°.

The first design shown has an order of 8.

The order of rotation in the second design is 10.

Order and Angle of RotationThe angle of rotation actually

measures the minimum angle required in order to turn the shape onto itself. It can also be stated as a fraction of a turn.

This picture has an order of rotation of 4its angle of rotation is 360 ÷ 4

= 90°The fraction of turn is ¼

Order and Angle of RotationThis picture has an order of rotation of 3.

its angle of rotation is 360 ÷ 3 = 120° The fraction of turn is 1/3

Time to playThis website is AWESOME for playing with

rotational symmetry. It has basic explanations, interactive examples, a symmetry artist activity and much more!

Check it out – what could be better than a website called “Math is fun”?

http://www.mathsisfun.com/geometry/symmetry-rotational.html

Time to practice:Page 21: # 4, 6, 7, 10, 12,14, 15, 17, 20, 24