Saturday, October 10, 2009

"Unconventional" measurement methods

I have been thinking about doing a mini Geometry unit on non-conventional measurement methods. My inspiration comes from the fact that, in order to measure the exact height from the second-floor balcony to the ground, I had to tie a string to a weight, lower the weight to the ground while keeping the string taut, and then measure the length of the string afterwards. (I was measuring the height in preparation for an Algebra 2 linear regression project.) There are other "non-conventional" measurement methods, such as using water to measure an irregular volume, that my 9th-graders almost certainly are not familiar with. Same goes for measuring perimeters around irregular shapes using a string or a rope. I think the mini unit has potential to be really fun for the kids, and also very educational / directly relevant to our Geometry content strands. :)

After some quick brainstorming, I recalled vaguely a classic puzzle of how to measure the weight of an elephant. I guessed that it would involve using buoyancy / weight of displaced water*, which, after looking the problem up on the internet, is indeed one standard way of measuring something that heavy. That might be cool to teach the kids. Another really awesome story that I found while looking this up was the story of the Chinese emperor who received advice from a kid for weighing an elephant. They sort of do use buoyancy, but in a much more intuitive / elegant way! I think my kids would dig that.

...Some days, I love teaching Geometry. It's pretty funny, because Geometry was my least favorite math topic in high school! (I did like it in grad school though.)

*Another way of doing it, I think, is to use pulleys to keep dividing the weight, until you can suspend the elephant in the air. But, that would take a whole lot of pulleys...


  1. more on geometry:

  2. Love it! I relayed the joke to Geoff and there was that awkward pause, same as in the comic strip.

  3. I think I would have liked Geometry better in high school if you'd been my teacher. :-)