Teaching Models

Perimeter, Area, and Volume

The perimeter of a polygon is the distance around it, or the sum of the lengths of its sides. Since perimeter is a length or distance, the unit of measure may be inches, feet, yards, centimeters, or meters.

Perimeter and Area
perimeter = 2 + 6 + 1 + 5 + 2 = 16
The perimeter is 16 cm.

In a plane, a simple closed polygon encloses a region that can be assigned a number called the area. The area of a region can be thought of as the number of square units, or parts of square units, that are required to cover the region without overlap. For example, the rectangle in the picture below can be covered with 6 square units, and therefore has an area of 6 square units.

6 square units

If, for example, the unit used for measuring length is the inch, the area is expressed in square inches. If the unit used for measuring length is the centimeter, the area is expressed in square centimeters.

Volume
A solid, or three-dimensional, figure occupies a region in space to which we assign a number called the volume of the figure. The volume of a solid figure can be thought of as the number of cubic units, or parts of cubic units, that are required to make up the figure without overlap. The volume of the rectangular prism below is 12 cubic units.

Volume

If the unit used for measuring length is the inch, the volume is expressed in cubic inches. If the unit used for measuring length is centimeter, the volume is expressed in cubic centimeters.


Teaching Model 17.4: Find Area


Houghton Mifflin Math Grade 3