Bubble Circumference

In celebration of Pi Day, I got my students practicing measurement, multiplication of decimals, and circumference....all using bubbles!

Now, let me preface this by saying that learning the circumference of a circle isn't actually a 5th grade standard in California.  That doesn't appear until 6th grade.  BUT, multiplying decimals is...SO we went with it.

The first thing I did was introduce the concept of circumference being the same basic idea as perimeter. Only it applies to a circle instead of a polygon.  We discussed the formula, the idea of Pi, and how it was used in the formula.  After doing a few samples, we headed outside.

Using the circles painted on the floor of our playground, I walked the diameter of one of the bigger circles, foot in front of foot.  It was *about* 17 Mrs. Moorman feet long.  Then, we did some mental math to figure out that the entire circumference of the circle, if I was correct in my explanation, should be *about* 51 Mrs. Moorman feet long.  I walked around and, what do you know, it took me 51 steps (foot in front of foot) to get around!  The kids were amazed....and convinced.

I let them walk the diameter and circumference of the circles around the yard as well, and when it all came out to be *about* 3 times the diameter, the idea was cemented for them and we headed back inside.

Now came the really fun part.  Each pair of students (they used their partner match up sheets...boy those things have come in handy!) was given a plate covered in tinfoil, two straws, a ruler, and bubble solution.  They were instructed to blow bubbles into the solution to create circles.  They sure got a kick out of that!

Once the bubble burst, it left a ring that was visible for a few seconds.  The students then used their rulers (they made the choice to use cm or in) to measure the diameter of the circle.  With that information in hand, they calculated the circumference of the bubble circle and started all again.

I didn't give the students an recording sheet (mostly because our copy machine is broken) so they chose to organize their information any way they saw fit.   Here were a few examples.

But, in case you would like a page to give the students (I know that sometimes just giving them an organizer helps to get them more on task), here is one for you.

We did this on Pi Day, but you can really do it any time throughout the year.  When you are working on multiplying decimals, introducing diameter, discussing circles and their place in geometry, or just want a fun math activity...this will fit right in!


  1. Wow! You really made it real for them. That is awesome!

    Your Africam lion story was great. Our internet was down at school today so no penguin cam. :(

    Marvelous Multiagers!

    1. They were playing the Penguin cam on Discovery (or something) this morning. Totally made me think of you!

  2. I just love your ideas! Your blog was one that inspired me to start mine! I downloaded (bought) all of your calendar math and adapted to our state standards and classroom needs. Would love to share that info on my blog, with proper credit and link of course, if you don't mind?

  3. What an amazing idea! Your ideas are always so great!


  4. I love this! I'll have to remember this idea the next time March 14th rolls around. Thanks for sharing :)

    Loose Shoelaces

  5. Very cool activity. Your kids are lucky to have you for their teacher!

    1. Here I am with the definition and formula of circumference of circle the circumference of a circle is same as the perimeter that is the distance around the outer edge.
      The formula of circumference is = 2 pi r (pi's symbol)
      where r = the radius of the circle
      and pi = 3.14(Approx)
      Circumference Formula of a Circle

  6. Thank you for an amazing idea!

    Here I'm sharing free online math tutoring website for students help. Must check out this:

    Free Online Math Tutoring


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