Lesson 1

Investigating Perimeter and Area

Est. Class Sessions: 2

Developing the Lesson

Part 1: Walking the Perimeter

Introduce Antopolis on the first page of the Investigating Perimeter and Area pages in the Student Guide. This ant town will provide a fanciful focus for much of the discussion in this unit.

Provide each pair of students with a piece of string. Explain that the ants in Antopolis only walk along the sides of shapes. They never walk across the center of a shape. They walk only on the perimeter. Perimeter, in everyday language, can mean the edge all around a shape. In mathematics, it is the distance around the shape. Using string to estimate perimeter reinforces the idea that measuring perimeter is measuring length.

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Encourage students to use the mathematical terms perimeter and area so that they become accustomed to differentiating between the two concepts. Similarly, ask that they identify the units appropriately; that is, square units (e.g., square inches, square centimeters) when discussing area and units of length (e.g., inches, centimeters) when discussing perimeter.

Ask students to find objects in the classroom that the Antopolis ants can walk around to find the perimeter. Have students use their string to measure the perimeter around one face of an object and decide if the string is longer than or shorter than the perimeter. Use small objects found in the classroom—books, game boxes, pencil boxes, etc. Students place the string around the object so that it outlines the shape of the face being measured. See Figure 1 for an example. Prepare a class display of a two-column data table. After students have measured the perimeter of their shapes, have them record the comparisons in the two-column data table. See Figure 2.

Ask:

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  • What shape did your ant walk around? (The front cover of a book, the circle at the top of a can, top of pencil box, etc.)
  • Can you show the perimeter of the shape using the string? (Possible responses: Yes, because my string fit around the shape with some left over. Or, no, because my string was not long enough to go all the way around my object.)
  • Is the perimeter shorter or longer than the string? (Depending on the object used, the response could be “shorter” or “longer.”)
Student Guide: 52
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SG_Mini
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Student Activity Book:
Master:
Measuring the perimeter of the top face of a tissue box using string
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Sample table with shapes sorted by approximate perimeter
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