The Four Planes of Symmetry Kallia Katsampoxaki- Hodgetts University of Crete 2012
Dec 24, 2015
The Four Planes of Symmetry
Kallia Katsampoxaki-Hodgetts
University of Crete 2012
Symmetry
A repeating pattern in a plane. A pattern is symmetric if there is at least one symmetry that leaves the pattern unchanged.
Symmetries
In mathematics, the idea of symmetry gives us a precise way to think about this subject. We will talk about plane symmetries, those that take place on a flat plane, but the ideas generalize to spatial symmetries too.
Types of Symmetry
Translation Rotation Glide Reflection Reflection
Translation
Translation Properties
A translation is defined by its direction and/or distance. Two objects are symmetrical under translation if one can be superimposed on the other such that their edges match up perfectly.
A translation
It is a shape that is simply translated, or slid, across the paper and drawn again in another place.
It shows the geometric shape in the same alignment as the original; it does not turn or flip.
Rotation
To rotate an object means
to turn it around. Every
rotation has a center and
an angle.
Rotational Symmetry
Rotation is spinning the pattern around a point, rotating it. A rotation, or turn, occurs when an object is moved in a circular fashion around a central point (i,.e origin) which does not move.
Formally, rotational symmetry is symmetry with respect to some or all rotations in m-dimensional Euclidean space. Rotations are direct isometries, i.e., isometries preserving orientation.
Rotation
Symmetrical object under Rotation
It appears the same when rotated about its center some fraction of 360 degrees. The most common types of rotational symmetries are 90 and 180 degree rotations, but others such as 45 and 60 also occur. For example, the number "6" is symmetrical to the number "9" under 180-degree rotation.
Reflectional Symmetry
Reflection symmetry, line symmetry, mirror symmetry, mirror-image symmetry, or bilateral symmetry is symmetry with respect to reflection.
A type of symmetry in which one half of the object is the mirror image of the other.
In 2D there is a line of symmetry, in 3D a plane of symmetry. An object or figure which is indistinguishable from its transformed image is called mirror symmetric.
Reflection
Symmetry about a vertical line of
reflection.
The hexagon has reflectional symmetry about both horizontal and vertical lines of reflection.
Related Terms for Reflectional Symmetry
Flip Horizontal Line Vertical Line Mirror Symmetry
Reflection symmetry, line symmetry, mirror symmetry, mirror-image symmetry, or bilateral symmetry is symmetry with respect to reflection.
Properties of Reflections
Reflections exhibit 1. Collinearity2. Betweenness3. Distance --length or linear measure4. Angle measure
Reflections do not preserve orientation. Reflections reverse orientation.
Solve a Problem
The letter B has reflectional symmetry. Identify the list of other alphabets with similar reflection.
Choices:1. A, H, I, M, O, T, U, W, X, Y2. C, D, E, H, I, O, X3. F, G, J, L, Q, R, S, Z4. A, B, C, D, E, H, I, K, M, O, T, U, X, Y
Steps before the Solution
Step 1: A reflection flips the figure across a line. The new figure is a mirror image of the original figure.Step 2: The alphabet 'B' has horizontal reflection because half a figure is a mirror image of the other half.
Solution
The other alphabets with similar reflection are C, D, E, H, I, O, X.
Glide Reflection
Glide Reflection
Glide reflection is the only type of symmetry that is a combination of two symmetries. It combines a reflection with a translation along the direction of the mirror line. It is also the only type of symmetry that involves more than one step.
Glide Reflections
In glide reflection,
Reflection and translation are used concurrently much like the following piece by Escher, Horseman. There is no reflectional symmetry, nor is there rotational symmetry.
Tesselations
If you look at a completed tessellation, you will see the original motif repeats in a pattern. One mathematical idea that can be emphasized through tessellations is symmetry.
There are 17 possible ways that a pattern can be used to tile a flat surface or 'wallpaper'.
Find the symmetry
References
http://math.hws.edu/eck/math110_s08/symmetries/index.html
http://mathforum.org/sum95/suzanne/symsusan.html
http://www.csun.edu/~lmp99402/Math_Art/Tesselations/tesselations.html
http://www.ehow.com/info_8465413_different-kinds-symmetries-math.html
Task 1: True or False?
Plane symmetry means a symmetry of a pattern in the Euclidean plane; that is, a transformation of the plane that carries any directioned lines to lines and preserves many different distances.
A pattern is symmetric if there is at least one symmetry that leaves the pattern changed.
In 2D and 3D there is a plane of symmetry. An object or figure which is indistinguishable from its
transformed image is called mirror.
Task 2:Complete the gaps
1. An object that is symmetrical under reflection is the ………..of the other object. Objects with reflectional symmetry are categorized by the ……….of the axis of symmetry: vertical, horizontal or slant. For example, the letter "W" has reflectional symmetry with the letter "M" along a ………axis.
2. Rotation is …….the pattern around a point, rotating it. A rotation, or turn, occurs when an object is moved in a …………..around a central point which does not move. 3. Symmetry under translation refers to simply moving the object horizontally, vertically or both ………rotating or reflecting it. A translation is defined by its direction and/or….. Two objects are symmetrical under translation if one can be ……….on the other such that their edges match up perfectly. It shows the geometric shape in the same a…….. as the original; it does not flip.4. ……reflection is the only type of symmetry that is a …...............of two symmetries. Two objects are symmetrical under glide reflection if one is a reflection of the other and is translated …………….the axis of symmetry.
Task 3: Dictogloss
Step 1:
Listen to the instructor reading a short text on
the four planes of symmetry and take notes.
Step 2:
Reconstruct the text after comparing notes with
a partner.