## Wednesday, April 6, 2016

### Volume of a Pyramid: Proof by Play-Doh

This is the best idea I never had.

My colleague, Tom Chan, asked me in the Math Office this morning, "Where are you guys at?"

I told him, "We're on volume of a pyramid."

"Me too!" He's usually a pretty cool cucumber, so this caught me by surprise. He said, "We're doing proof of the volume formula by Play-Doh. Wait here a minute."

He dashed out and came back within a minute with a fist-sized cube made of three different colors of Play-Doh.

"Each table gets three little tubs (so three colors) and they have to make three identical pyramids that fit together into a cube. Then they can move on and do the next piece."

I was dumbfounded. The best I'd been able to do for today was to produce tiny, helpful diagram handouts to fit into our INBs.

But I'm bookmarking this for myself for next year by blogging it, and by giving full credit.

#### 7 comments:

1. That sounds like a lot more fun than pouring 3 scoopfuls of sand in a plastic pyramid into a cube. I think that experience would be a lot more memorable (kinesthetic not an observation).

2. Now I know what my colleague and I will be doing this afternoon during planning! Thank you for sharing.

3. CPM has foldable nets of pyramids that fit together as a cube.

1. Do you have access to these nets?

4. Julie blogged about something similar a while back: https://ispeakmath.org/2012/05/28/volume-of-3d-shapes-with-play-doh/ and I have been planning on borrowing this brilliance for a while - to be realized next week! - Wendy

5. Definitely need to include this thinking from Julie Reulbach at I Speak Math: https://ispeakmath.org/2012/05/28/volume-of-3d-shapes-with-play-doh/

6. Hello! I am a student from UC Berkeley in the Cal Teach Program. I surprisedly found that we did similar things in our EDUC 130 class as your colleague did:) The difference is, instead of finding the volume, we were using Play-Doh to find the shape of the cross sections of a cube. We made Play-Doh into little cubes and actually cut it into two parts to see what the shape the cross section is and why is that. We found out that using Play-Doh is much more interesting than just imagining and graphing on the scratch papers. It helped a lot in understanding the property of the cube by visualizing the cross sections for us.