# The Euler Characteristic in Play-Doh

An Icosahedron

Notice that if you have a Platonic solid and you calculate the number of Vertices (ie. corners) minus the number of Edges plus the number of Faces you always get 2!  That is, you seem to have the following equation:

$V - E + F = 2.$

Is this a freakish coincidence or is this there something going on here?  Since we study math, we know that freakish coincidences usually mean there’s cool math lurking around.

On Wednesday, October 1st the aptly named Matt Clay of the OU Math Department will give a talk in the Math Club about Euler’s Formula and show how you can prove it using Play-Doh®.  The details are:

Speaker:  Matt Clay, OU

Title: A Convenient Truth: V – E + F =2

Abstract: Using Play-Doh, we will investigate Euler’s Formula V – E + F = 2.
Using Al Gore’s “Inconvenient Truth” we will give a proof.  Unfortunately,
Melissa Etheridge has declined to attend and perform her Grammy award
winning song “I Need to Wake Up (and Do Math)”.

The talk will be on Wednesday, October 1st at 5pm in PHSC 1105.  As usual, there’ll be free pizza! Unusually, there’ll be free Play-Doh, too.

If you’d like to print out the flyer, you can find it here.

Addendum: If you are interested in the “global warming” proof of Euler’s formula which Matt talked about yesterday, you can find it here:

http://www.ics.uci.edu/~eppstein/junkyard/euler/

The website has nineteen (19!) different proofs of Euler’s formula.  Matt used a variation on proof #14.  He also suggested the people check out proof #6 as another cool one.

Who needs a Large Hadron Collider for experiments when you have Play-Doh?

## 10 thoughts on “The Euler Characteristic in Play-Doh”

1. In chem, we were given the assignment, “Watch An Inconvenient Truth by Al Gore.” Now, it’s popping up on the math club. I suppose i really should watch that movie…
But I like Play-Doh, so i plan on attending.

Sincerely,
Scott Lowe

2. I had to do a research paper over global warming so I’m really familiar with The Inconvenient Truth. I think that it would be really amzing to see how to prove V-E+F=2 with play-doh

-Mike Nguyen

So, unfortunately I didn’t make it to this one – but I’m sure there will be additional exciting mathematical events in the future, which I will try harder not to forget to attend!

4. If there’s any extra free Play-Doh lying around some one should drop it off to Dr. Brady’s honors calc three class 🙂

5. It is a shame that i missed this. It is always interesting when math is tied into an unlikely subject, for instance global warming.
It shows just how powerful numbers can be.

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7. I really enjoyed this talk! I learned a lot, and the free play-doh was amazing! I think it would be very nice if the Math Club did more talks like this one. Learning while simultaneously having fun is the best way to learn!

Brandon Perkins

8. I wish I had been able to attend this! As a Math Education major, I always like to hear math topics being connected to real-life examples that people can relate to. This is one of the most important ways to get high school (and college!) students engaged in and interested in math (which is often quite a challenge!). I’ll be keeping my eyes open for other presentations like this one that might be able to give me ideas to use in my classroom someday.

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