Symmetry and Transformations (4/4)

 1. General Information 2. Translation 3. Rotation 4. Reflection 5. Glide Reflection 6. Hands-On Activities
Glide Reflections and Glide Reflective Symmetry
A last type of symmetry is glide reflective symmetry which results from the transformation called glide reflection.

A glide reflection is actually a combination of a reflection and a translation. Whether the reflection happens first or second does not matter. The figure that results after a reflection and translation is simply called the glide reflection of the original figure. (Notice how "glide" refers to the translation part of the combination.)

The same terms that apply to reflections and translations apply to glide reflections. An axis is needed to perform the reflection and a magnitude and direction are needed to perform the translation.

 In this example of a glide reflection, the reflection is performed first, and the translation performed second.

Here are two examples of glide reflections applied to some other shapes. The original shape together with its reflection is said to have glide reflective symmetry.

 Examples of glide reflections and glide reflective symmetry

What does it mean for a tessellation to have glide reflective symmetry? If we can perform a glide reflection to a tessellation that such that the result is the same as the original tessellation, then the tessellation has glide reflectional symmetry. An example is as follows:

 A tessellation that has glide reflective symmetry. To demonstrate why, it is first reflected along the red dotted lines. Then, it is translated until the newly made copy matches the original exactly.

(One interesting note for further explorations: Every tessellation that has reflective and translational symmetry also has glide reflectional symmetry. Do you see why? After performing the appropriate reflection, we can perform the appropriate translation. The overall transformation demonstrates that the tessellation also has glide reflectional symmetry. However, not all tessellations with glide reflection symmetry have reflective symmetry and not all have translational symmetry.)

 Real examples of glide reflective symmetry:

 After trying the hands-on activity, use the templates on the templates page to see why every regular, semiregular, and demiregular tessellations has glide reflectional symmetry. Use the technique that was explained in the hands-on activity.