What Shape Is A Flat Toilet Paper Roll?

What Shape Is A Flat Toilet Paper Roll?

Shapes

Converting things you have around the house from three-dimensional objects into two-dimensional flat shapes will surprise your grandchildren with how different things look when they’re flat.

Seedling in a toilet paper roll repurposed as ...
Seedling in a toilet paper roll repurposed as a mini planting pot (Photo credit: girlingearstudio)

Materials

  • Assemble empty containers of a variety of shapes that can be cut up. You are looking for cylinders, rectangles, cones, spheres and cubes
  • Cardboard cylinders, like toilet paper or paper towel tubes or salt or oatmeal boxes, or labels that wrap around a can.
  • Rectangles, like cereal or shoe boxes or paper lunch bags, some with ends cut off, some with ends on
  • Square Kleenex boxes or berry containers for cubes
  • Orange peel, whole for a sphere
  • Paper cone cup, or fold the corner of a paper towel into a funnel and cut off the top to make it even, then tape the seam
  • Scissors
  • Felt-tip marker or crayons
  • Newspaper

Instructions

  • Cut containers into open, flat shapes. To keep it simple, cut the tabs off that glued the sides together
  • Using the felt-tip marker or crayon, draw around each shape on the newspaper
  • Optional: Predict what shape a container will be before you cut it flat and draw it to see how close you get
  • Optional: Color one side of a container and predict where that colored side will be when you flatten it by drawing the expected shape before you cut it.

What Should Happen?

Very quickly, your grandchildren will see:

  • Cylinders, when flat, turn into rectangles. When the tops stay attached, they are circles
  • Rectangles, when flat, have one or two rectangles from the ends attached to the side of a big rectangle
  • Cubes open into four squares around a square, with an extra square attached to one of the outside squares for its top
  • Cones, when flat, are semicircles, with a circle attached for its top

Why Is This Useful?

Understanding what a flat surface looks like from a three-dimensional object makes it a lot easier to figure out its area.

The surface area of the toilet paper tube, for instance, is figured by measuring the width (height) and multiplying it by the circumference (length around).

This is much easier to see when you lay it out flat.

By the time your grandchildren find out there is a formula, area = height times 2 pi r (for radius), the formal way of calculating the area of a cylinder when you can’t lay it out flat, they will remember that a toilet paper roll is simply a rectangle.

 

Carol Covin, Granny-Guru

Author, “Who Gets to Name Grandma? The Wisdom of Mothers and Grandmothers”

http://newgrandmas.com

 

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Comments (5)

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  1. Susan Cooper says:

    Anytime scissors and glue are involved kids are engaged… LOl. This is such a fun exercise to teach that formula.

    • carolcovin says:

      It's almost like magic, to think that a cylinder can become a flat rectangle, and kids do like to work with their hands!

  2. JeriWB says:

    Once again, an activity that would have been great for me when I was a wee one. I grew up to be a totally geometry phobic 😉

    • carolcovin says:

      It seems harder on paper than when you are manipulating physical objects, like a roll of toilet paper!

  3. Susan Oakes says:

    Love your creativity Cheryl and this does look like fun for kids.