Thursday, September 22, 2011

A Win for Prototyping!

Physics did the Timer Challenge this week - they were tasked with using an oscillator (though we hadn't used that word yet) to measure time.  After 40 minutes of work or so, I cam around and put a piece of tape of each group's stopwatch, wrote a time on it, and gave them a few minutes to prepare to measure that time interval using only their oscillators.

This is great for science: jumping in, experimenting, finding out new things (not confirming things that I told them), and, ultimately, owning a task that they didn't necessarily know how to complete less than an hour ago.  I mean owning, by the way: my Physics Hall of Fame records a group in 2009 with .06% error on this one.  Most groups get under 1% error here.

Many things were discovered, including some of their own misconceptions: didn't that spring "slow down" when the motion got smaller?  Why doesn't the time for 10 cycles change when I keep changing the pendulum's mass?  

Some groups try the "easy way out" - getting the period to be a second or 2 seconds (they don't really know what period is at this point, so some pick half a cycle as their unit).  It's best to make the setups resistant to this.  That's pretty easy with the inertial balance and mass/spring, but requires relatively short pendula.

The first period of this went about as expected; most groups come up with some sort of proportion/cross-multiplication type of method, once they figure out that the rate of oscillation doesn't really change.  Usually, that conclusion is just based on a couple of measurements or eyeballing.  (Frequently, the eyes lie, and I might prompt with "if it's so obvious, then I bet you can prove it easily.)

The second period of this saw an outbreak of modeling, though: graphs were drawn, relationships were proposed, variables were written with good symbols, and constants found units and values.  All in all, it was awesome.

The genesis of those graphs was genuine - I didn't require the graphs.  They (I witnessed the graph-decision-moment for at least two of the groups that I saw drawing the graphs) couldn't quite decide what happened to the oscillator as its motion got smaller, and decided that graphing the time required for different numbers of cycles would tell them what was going on!

Here's one of these graphs:

They're not just making models here - they're revising them and making them ever more communicative!  You just can ask for anything more on a Wednesday than that.

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