In fourth grade, students are expected to understand that polygons are plane figures with closed shapes and straight sides. They learn to distinguish between polygons and other types of shapes such as cubes, prisms, cones and circles. Students define, classify and compare polygons, describing them using vocabulary such as vertex, edge and congruent. Activities should include many opportunities for students to analyze geometric shapes and real objects to determine if they are polygons.
You can create an anchor chart about polygons for the class while students explore straight-lined shapes, creating polygons. This activity will also reinforce vocabulary that can be added to the class chart. Give each student several toothpicks or craft sticks to use as the straight sides of polygons. Students could use a math notebook to create a copy of the class anchor chart for their own studies. As they explore and create polygons with the sticks on tables, have students describe and share the closed, straight-sided shapes they create as you add them to the anchor chart. As each is added, have students count the number of sides and vertices. Add these to the anchor chart and student charts. Discuss vocabulary -- that a pentagon is a five-sided polygon, and an octagon is an eight-sided polygon. This vocabulary and an object with that shape should also go on the chart.
Students can go on a polygon scavenger hunt using a clipboard, paper and pencil. Instruct students to create a chart on which to note the polygons they find. The chart headings should be Type of Polygon, Number of Sides, Illustration. Take students outside as a group to explore the playground and schoolyard for polygons to chart. Students can also go in groups to explore the building halls, library, gym, offices and cafeteria looking for examples of polygons. Once back in the classroom, combine the results of the polygon scavenger hunt to create a class polygon chart.
Describing and Comparing Polygons
Show students examples of basic polygons such as hexagons, quadrilaterals, trapezoids and triangles. Ask students to find ways that some of the polygons are similar and share their findings. Students might respond, for example, that quadrilaterals and trapezoids both have four sides and four vertices. Another student response might be that squares and rectangles both have four sides, four vertices and four congruent angles. Instruct students to create a foldable item that labels and describes each polygon according to the number of sides, vertices and congruent angles it has. From the foldable, you can have students create flash cards for use in studying the characteristics of the different polygons. On one side students draw the polygon and on the other they describe it. To play, students look at the polygon drawing and name its characteristics.
Allow students to use their creativity to show you that they understand polygons. Provide them with directions for completing a drawing made of polygons. Explain that if everyone follows the directions exactly, they should all have roughly the same drawing when finished. For example, instruct students to place a closed, two-dimensional shape with four congruent angles and straight sides all of 3 inches each in the middle of their paper. On top of this shape, they should draw a two-dimensional shape with three sides and three vertices. After following the directions and creating the polygon art, have students compare drawings to see if everyone created a similar picture, since all had the same directions. After this activity, allow students to create an original piece of polygon art.
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