Sunday, August 26, 2007

Surface Area Activity

In a workshop last Saturday we did a cool activity that I have to share. It wasn't new to some people, so maybe I'm the only one who's never seen it. Each group of 2-3 people was given an orange (try to get them as spherical as possible), some wrapping ribbon (or string, something to measure the circumference with), a compass, a largish blank sheet of paper, and a calculator (later she made sure there were wet wipes to clean with). We were going to estimate the surface area of a sphere.

1. find the circumference of your orange with the ribbon. Be accurate.
2. using this measurement and prior knowledge, find the radius of the sphere.
3. with the compass draw 6 or so circles with that radius.
(teacher checks the circles before kids proceed by placing orange on top of circle and eyeballing)
4. peel the orange and fill as many circles completely as you can. (only the "orange" part is the surface area)

It was great, we fit exactly 4 circles, (which are of area pi*radius*radius), so voila we had an estimate of the surface area. Ooh aah.


  1. Cool. I'll try it myself today, and find a way to sneak it in to some class, at some point in the future.

    I'm so glad we no longer give the kids those lousy little oranges for lunch. They don't taste so hot, and the peel always came off in little pieces. No, if I do this I will have to invest in proper oranges for all.

  2. Anonymous9:56 PM

    Hi Jonathan,

    Our instructor mentioned that if you use the oranges with the thicker rind, make sure to have a discussion with the students that the "white" part of the peel is not part of the surface. Other than that, it WAS fun.

    Ms. Cookie

  3. Good idea! I can't wait to use this lesson in my geometry class at the end of the year. I love to have hands-on activities for my students, they seem to retain the information more.

  4. This is an excellent idea, and I will definitely try this when doing surface area with my geometry class. If you have any great hands on activites with triangles please share them with me.

  5. myla b.12:34 PM

    wow! got lucky of finding this blog. i will try this strategy with my students. thanks!

  6. ruchi sharma12:56 AM

    hi its Ruchoi here . your idea is wonderfull. I m a teacher trainer . I was looking for an activity for this topic. I came across your idea & i would like to share it with my pupil teachers. thanks.