Monday, October 02, 2006

More on the HOBO g-pendant

I posted about the new G-Pendant from the HoboDepot last week. I showed an experiment some of my students were conducting relating to the benefits of shoes for absorbing shock rather than transferring it to your knees and back.

The maximum g-force on the graph was above 5 g's (The maximum possible reading is 3 g's in any one direction). We were graphing the sum of the three axies rather than just the x direction (straight down). Birch, a retired physics teacher pointed out we may have been maxing out the pendant in one of the component directions. Well, he was right. We went back and analyzed the data today and found with no shoes we did max out the g-force in the x-direction. With shoes we only maxed out for a few of the steps.

We played some more and found it is hard to keep under 3 g's. With this limitation it is still possible to do some good labs.

We put the sensor on the inside edge of a roll of masking tape and rolled it. You have to roll it really slow to avoid maxing out centripetal force. However, it is easy to see when each rotation happens. So, we rolled it down a ramp and were able to calculate acceleration. With a roughly 20 degree angle we were able to estimate acceleration to an acceptable 10% error. Any steeper and we would have maxed out too fast to collect any usable data (we'll confirm this later).

Tomorrow I'm going to have them do periodic motion, both pendulum and bouncing on a spring.

In case you're wondering. I have a few highly motivated students who have eighth hour off and like to hang out in the physics room (who doesn't really?), so I've put them to work.

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