wheel symmetry what you need to know to understand this type of symmetry
Post on 31-Dec-2015
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Wheel Symmetry
What you need to know to understand this type of symmetry
Basis of these symmetry groups
• Circles– How many degrees in a circle?– Importance of the radii and the diameters?– The role of the center of the circle
Basic Properties of Circles
• All circles comprise 360 degrees
• A radius is a line segment with one endpoint on the circle and the other endpoint at the center of the circle
• A diameter is a line segment whose endpoints are on the circle and intersects the center of the circle
One type of symmetry that occurs
• Rotational Symmetry– There must be an angle that the shape is rotated
through and a point about which the angle is centered
• The angle of rotation is the angle between two radii of a circle
• The center of rotation is ALWAYS the center of the circle
A possible type of symmetry
• Reflective Symmetry– A line that acts as a mirror may be present– This line must be a diameter of the circle
Classifying the Symmetry Groups
• Only rotational symmetries are present– These groups are called CYCLIC– Each of the rotations are by the same number of
degrees
Classifying the Symmetry Groups
• Rotational and reflective symmetries are present– These groups are called DIHEDRAL– All rotations are by the same degree
measurement – There is a mirror along each rotational radius
and halfway between each radius– There are the same number of mirror lines as
rotations
Notation to represent the groups
• Cyclic groups– Named by the number of rotations
• Four 90 degree rotations: C4
• Ten 36 degree rotations: C10
• Dihedral groups– Named by the number of rotations (Note: there are the
same number of reflection mirrors)• Three 120 degree rotations and three lines of reflection: D3
• Six 60 degree rotations and six lines of reflection: D6
Examples of Wheel Symmetry
• The picture to the right is of an automobile hubcap. It represents a wheel symmetry called D5.
• There are five rotational symmetries and five lines of reflection.
Examples of Wheel Symmetry
• This hubcap is an example of a C7 symmetry
• There are seven rotations each measuring 360/7 degrees (or 51 3/7 degrees)
Examples of Wheel Symmetry
• This hubcap is an example of a D8 symmetry
• Do you see the eight 45 degree rotations and the eight lines of reflection?
Which symmetry groups are seen below?
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