The Earthquake Lab

Waves are tricky to teach. Students feel like they already have a ton of experience with them (you've been to the beach somewhere, I'm sure.) and that there isn't a whole lot more to learn. So, I try to make it hands on and connect with other areas of interest.

For instance, I brought my guitar into school. Music is waves working well together. So, I fiddled around during class while they were working and had them make connections between the guitar and the theory of waves. A few days later, I moved into a NOVA episode about the 2011 Japan earthquake and resulting tsunami...more waves. Students were able to connect the abstract - longitudinal and transverse waves - with the concrete - P and S seismic waves. At this point I introduced the earthquake lab.

The Setup

Students broke into teams of four and assigned roles - Project Manager, Treasurer, Research Director, Architect - based on their interests. Their task was to build a building at least 40cm tall out of spaghetti, marshmallows, and tape which would stand up to an earthquake. I modified this doc (Word download) and gave one sheet per group.

The Challenge

When I assigned this task, I said the structure had to be at least 40cm tall, but I didn't tell them that it should be as tall as possible. Some groups naturally went for it (one group hit 98cm!) while others played it safe. Next time, the height challenge will be added.

Also, if you look at the document, I dropped the line of credit to $4000, thinking it would make them think through their designs. I also limited their trips to the store (me) to two visits to really make sure they designed. Nearly every group was very intentional, but I still wish I had added the "economy" challenge to the height: tallest building you can make (at least 40cm) while staying cheap. Things to remember for next year...

The Shaker

The final hurdle was designing an earthquake machine that would shake every building fairly. I also wanted them to see the difference between P and S waves, so it had to shake on two axes. I tried to work through a couple of ideas which would have required cranks, drills, drawer sliders, and lots of engineering and instead landed on something sweet and simple: a tone generator on our LabQuest sets and a hacked apart speaker.

IMG_20160202_154302 P Wave arrangement. Speaker is mounted below the platform.

IMG_20160202_154444 S Wave arrangement: lateral speaker with the LabQuest hooked up.

I used some 10-gauge house wire and industrial strength hot glue to add some hooks to the speaker baffle. A small power source let me control the volume of the tone being generated. I drilled holes through a small whiteboard to mount on top of a speaker (P waves) and beside a speaker (S waves). We ran the P waves at around 25Hz and the S between 10-12Hz. The goal was to show students how properly-built buildings resonate with the shake, not fight against it.

It gave a pretty good speakers this year were a little small, but it worked well to show resonance. I think if we went for height next year, we'd get a few more building failures, which are just as important as building successes.

Thanks to Anthony Purcell for making sure I wrote this up. Leave a comment if you want tips on building your shaker.

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