Sunday, May 25, 2014

Going Round In Circles

Whenever I start talking about circles with my students, I use this little wager.

I get students to pick one of the three choices and work the room, looking for a brave student I know will deliver my nachos. I talk up the nachos (and the circumference) as much as possible. Anywhere from 90 to 100 percentage of students will say the circumference is shorter than the height of the water bottle. Let's see if I win nachos or I let my students go to lunch early.

Okay, so double or nothing? I don't bring in this glass, but I do use a taller cup with a really small circular base. Where do you stand on the double-or-nothing wage? Did I give you enough information to take the bet? With a glass like this, you should get at least one student to keep you honest and ask which circumference of the glass you'll be measuring.

This little wager (activity) allows me a quick introduction and fun application of circumference. Somewhere I'll discuss vocabulary and formulas with students while giving them a graphic organizer they can fill out.

I'll usually do an activity where students measure the circumference and diameter of objects in order to discover the relationship of Pi. Stuff very similar to Fawn's Friday Bubbles. Note to self, use Excel (or a spreadsheet) to keep track of those measurements. I've also explored Rolling Tires in the past. This year, I brought the wheel to the class for a small activity. A physical wheel. The wheel from my son's wheelbarrow.

The small activity was for students to guess how many rotations this wheel (8-inch diameter) would make from one wall of my class to the other wall. Students were able to see how circumference can take on the meaning of a tire rotation, hence the graphic I made above. It was sweet to see students roll the wheel across my 21-foot long room and actually get 10 rotations like the math predicted. If you have a wheel like this, bring it in and do this activity.

We also did these awesome lessons. And. I. Mean. AWESOME!
Pizza Pi by Mathalicious and
Penny Circles from Team Desmos and Dan Meyer.

There's so much to do with circles and so little time. 

Round and round,


  1. Andrew,
    Wow! I thought I had a great lesson when I had the students rotate through stations measuring circular objects to discover the relationship between circumference and diameter. This goes way above and beyond mine! We are going to have 1:1 Chromebooks next year, so I like the idea of putting the data into a spreadsheet -- this will be a lot easier with the Chromebooks readily available. I really like the idea of bringing the wheel in to relate the circumference to the distance traveled. I am going to try to remember all of this for next year -- thank you for sharing!

    1. Hey Mathtechy,

      Thanks for stopping in and I hope you can use this next year. Yes, using a spreadsheet makes it so much easier for you and the students. I wish I had figured that out earlier.

  2. Freak'n awesome man. I'm currently writing units of study for my school district. I'm plopping that bad boy in right now.

    1. Right on! Thanks Tim!
      There's more to this lesson and the additional activities that have come out of this wager. I'll have to blog about it