Unit 1, Lesson 2
Naming the Moves
Grade 8
Preparation
Lesson Narrative
In this lesson, students are introduced to the terms translation, rotation, and reflection and begin to describe these transformations with greater precision. The collective terms “transformation” and “rigid transformation” are not used until later lessons. Students are also introduced to the terms clockwise and counterclockwise. Students then use this language to identify the individual moves on various figures.
Students engage in MP6 as they experiment with ways to describe moves precisely enough for another to understand their meaning.
- Describe (orally and in writing) the movement of shapes informally and formally using the terms “clockwise,” “counterclockwise,” “translations,” “rotations,” and “reflections” of figures.
Let’s be more precise about describing moves of figures in the plane.
Required Preparation
Make sure students have access to items in their geometry toolkits: tracing paper, graph paper, colored pencils, scissors, ruler, protractor, and an index card to use as a straightedge or to mark right angles.
Access to tracing paper is particularly important. Each student will need about 10 small sheets of tracing paper (commercially available “patty paper” is ideal). If using large sheets of tracing paper, such as 8.5 inches by 11 inches, cut each sheet into fourths.
The word clockwise means to turn in the same direction as the hands of a clock. The top turns to the right.
This diagram shows that Figure A turns clockwise to make Figure B.
The term counterclockwise means to turn opposite of the way the hands of a clock turn. The top turns to the left.
This diagram shows that Figure A turns counterclockwise to make Figure B.
A reflection is a transformation that “flips” a figure over a line. Every point on the figure moves to a point directly on the opposite side of the line. The new points are the same distance from the line as they are in the original figure.
This diagram shows a reflection of A over line that makes the mirror image B.