Aw Pi day……a day to eat pie. Well, it is circular…..

###### Photo courtesy LeJyBy at Flickr Creative Commons

But if you’re a math teacher like I am, we get kinda giddy about this day. I like to use it to answer the age old question of, “Why is Pi 3.14?”

This is a really simple activity you can do with your students too. It requires different sized circles (I bring in cans), cm grid paper, scissors and masking tape.

I usually put my kids into pairs and then the activity goes something like this:

**Step One**

Place the bottom edge of one of your cans/lids/circular objects at the base of the cm grid paper and trace it. Now, count the height of your circle (estimating as best you can)….this is also a great time to talk about how this is the diameter of the circle.

**Step Two**

Have students wind masking tape around the outer edge of the circle (the circumference) – trying to get the edges of the tape to match up as precisely as they can. The scissors help here.

Take the masking tape carefully off the lid/can and place it on the grid paper next to the circle you just traced. Make sure the edge of the tape is right along the baseline and try to get it to go as straight up as possible.

**Step Three**

If you compare the ratio of the height of the traced circle to the height of the masking tape….students ultimately come out with an answer very close to 3.14. Some of my kids actually got it bang on last year (well, if you cut off the rest of the continuing decimal places).

After all….the formula for circumference of a circle is

C= Pi * d

So it makes sense that C/d = Pi

And if they repeat this with different sized cans/lids (I try to get them with at least three different objects) they will see that this ratio holds constant…..hence why Pi is 3.14.

Cool hey?

Sorry I don’t have pictures to go with this blog post! I will after tomorrow.

I am going to try these with my 5 th grade on Friday. Thanks for sharing!