Inquiring the Surface Area of a Sphere Through the Peeling of Oranges!

It's getting closer to the winter break, so it was great to have some hands-on activities to add some spice to the classroom for my academics.

It seems like my applied class is getting all the engaging and interesting approaches to math, so this was quite refreshing for myself (and especially these academic kids) to have this tangerine activity to explore the surface area of a sphere.

First thing we did was take a good look at the tangerines and noted its differences from a perfect sphere.  We then went on to talk about how perfect mathematical spheres don't exist in the real world since once one gets into the atomic level, things just aren't continuous.  This sort of statement really bothered some of my students  that one went home and told their parents.

Nevertheless, upon noting the clementines' (lack of) sphere-like properties, we proceeded to take a guess as to its surface area in terms of its radius, and thus area of its 2D ('projection'?)  version.   Each partner made their guess:

Looks like they their estimation skills are almost en par with my applied students' skills which has been honed through the Dan Meyer's 3-act process.  That...or they looked at the formula sheet or remembered the answer from their elementary school days.

Let's see how they did:

 I guess they couldn't be bothered to peel that other portion there to get its true surface area?  I guess I should have done more teaching and less snapping of pictures here, as I could have demonstrated that by peeling the skin into smaller pieces would more accurately depict the surface area.  Right now, much of the 'surface' area is used for the third dimension of height severely downplaying the true surface area of this orange. 

 That clementine there looks quite tasty.  I must mark these students' self regulation skills to be excellent in their ability to stay on task without eating some juicy fruit.

 Now that clementine looks quite symmetrical...and tasty.

Ahh, "four" circles!  The 'true' answer.

Now this group featured a student who made the best notes ever and another student drew some of the best art on evaluations.  The illustrations left behind were both profound and thoughtful.  It's no small wonder that they took the time to rip the orange peels into symmetrical sizes to create the above work of art.

Anyways, this activity proved to be quite memorable.  It's a good one and one that I'll continue to do every time I teach grade 9 as it somewhat demonstrates how the surface area of a sphere is 4πr^2 or the equivalent of the area of four circles.