String Circumference

Objectives

• Understand and measure circumference of a sphere.

Materials

• Per Student:
  lengths of string, cut to fit around at least the largest ball

• Per Group:
  a variety of different-sized balls and/or spheres (e.g. tennis balls, basketballs, golf balls, fruit, etc)
  Unifix® cubes  or Duplo®/Lego® (optional – for further measurement)

Key Questions

• What ball has the smallest circumference? Largest? (How many cubes long are they?)
• What else can we use to measure circumference?Can you put the balls in order, from smallest to largest circumference?

What To Do

1. Wrap your string around your ball.
2. Make a mark with a felt pen where the end of your string touches the rest of the string.
3. Stretch out your string and see where the felt mark is. This is the circumference.
4. If available, line up interlocking Unifix® cubes all along the circumference-length of string. How many cubes ‘long’ is it?

Extensions

• Try measuring the circumference of other spherical objects. If it's around Halloween, pumpkins are a great option.
• Go on a neighbourhood exploration for circles and spheres, or have students bring some items from home (e.g. toilet paper rolls, a can, etc) to measure their circumferences.
• After some practice, try predicting circumference. Collect other round objects and make a 'prediction mark' on your string with a different colour felt pen, then measure it and mark the actual circumference. Try a few times to see see if you improve.