Monday, July 2, 2012

Chains of Reasoning: Standing Waves and Tension

I'm clearing out a few "meant to" posts from the year.  Here's a chain of reasoning problem I had kids do about a slinky hanging from the ceiling. I asked this as the 'advanced' question on their big waves assessment, and we came back to it in groups the next day. Students were asked about what would happen to the frequency, wavespeed, and wavelength of the waves from the top of the slinky to the bottom, and then to draw a standing wave diagram to reflect that.  I prefaced it with a question that elicited from almost everybody that the tension in the slinky was greatest at the top (almost 100% success even though they never studied forces - you just have to ask it specifically for them to realize it).

Since most had trouble with the question, I wanted them to work through it, rather than just forget it and move on.

The whiteboards are below. I was very particular with them writing down all of their reasoning - mostly "how do you know that's true?" and "what did you observe or assume to get to that?".  If I stayed on them, they did well and their answers were all correct! It's a year-long process to get them to internalize that process. It's not that they don't have the ability, but being a true self-critic is much more difficult than giving up.

 Hmmm... I can't get this one rotated - Blogger issue.  The original's fine!

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