Elementary Geometry: Working with Rectangular Prisms

Using Rectangular Prisms in Elementary Geometry

Finding Rectangular Prisms

A rectangular prism is basically a box; so many children will be familiar with the shape. However, you can introduce the concept of prisms to your son or daughter through books such as What in the World Is a Prism? by Anders Hanson or Prisms (Exploring Shapes) by Bonnie Coulter Leech.

Take your child on a hunt for items that look like rectangular prisms around your home or neighborhood (i.e., a box of cereal or a brick). For extra learning opportunities, arm him with a ruler and encourage him to measure the length, width and height of each rectangular prism he locates. After the hunt, make a list of other rectangular prisms that appear in real life. To add breadth to your search, look for pictures of rectangular prisms in magazines and books.

Make Rectangular Prisms and Nets

Children can make prisms with unit cubes. Give your child 24 cubes and see how many different kinds of rectangular prisms she can make (she should be able to make at least seven prisms). Have her trace each of the sides on graph paper; she'll soon see that for each prism she has six drawings that can be grouped into three pairs of identical sizes. You may even have her write the measurements for each prism (e.g., 4' x 3' x 2').

Your child can then cut out her shapes and tape them together to make 3-D boxes. Conversely, she can tape the sides together to make a flat net of the prism, which is a 2-D illustration of a 3-D prism. With experience, most children will be able to draw the nets without having to first draw each side separately.

Once your child has built a rectangular prism, do experiments to determine what surface area and volume the rectangular prism has. The knowledge gained through these experiments is translated to formulas for volume (V = lwh and V = bh) and also for surface area (S = 2lw + 2lh + 2wh). (In these formulas l is length, w is width, h is height and b represents the area of the base.)

Read and Sing about Prisms and Nets

YouTube.com offers a variety of different songs that can help students learn about rectangular prisms, such as Volume Song, Surface Area Song and The Regular Objects Volume Song. Alternatively, you can connect your child's school work to the real world with the book Wrappers Wanted: A Mathematical Adventure in Surface Area by Candice Yarbray Brucke, in which Santa needs help to go green and save wrapping paper! Similarly, older elementary school students will enjoy learning practical applications of boxes or prisms from the Yup'ik Eskimos in the book Building a Smokehouse: The Geometry of Prisms by Melissa Kagle.