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27 September 2012

Just take the data! It works!

Left to their own devices, novice physics students get easily intimidated by laboratory.  They concern themselves so much with the precision of each measurement that they lose sight of the overall purpose of the lab.  How do we get students to just freakin' measure, for goodness' sake?

Sports analogy time:  I'm a baseball umpire.  When I work a game with players and coaches who have never seen me, they're sizing me up, figuring out what's a ball and what's a strike.  

Now, I generally work high school JV and 8th grade games.*  I call a wide strike zone -- a tight zone at a level where the pitchers can only aim the ball within a steradian or thereabouts leads to walk after walk, which is no fun for anyone.  So how do I establish this strike zone?

I don't talk about it.  I just call it and smile confidently.

Sure, I get a lot of stares some bad body language, even a few verbal complaints in the first few innings.  But it's amazing how quickly everyone sees what I'm doing.  They adapt.  By the fifth inning, the batters are swinging more often; they aren't turning around when I call a strike on the outside corner.  And if they see me in a game a week later, they know what to expect right away.  I get a fun, action-packed, fast-paced game with few if any complaints -- all because I weathered the initial storm to establish my strike zone. 

* By choice, much of the time -- I've done varsity games, but at varsity they expect you to start perfect and get better.  The participants and fans at a lower-level game are so happy to see someone who seems relaxed but serious and competent that they don't complain or argue with me.  I've had even losing fans repeatedly thank me for my work as I'm leaving... that never happens at the varsity level.  

I start establishing the physics laboratory equivalent of the strike zone on the first day of class in conceptual physics.  We measure angles of reflection and refraction with a ray box, a protractor, and a mirror.  I call students to the front of the room to make the measurements and record data on the board; everyone else is in a seat making a graph as the measurements show up on the board.  Easy stuff, but we're learning:  we're learning that angles are measured from the normal, we're learning how to use a protractor, we're learning to graph as we go in lab... we're learning not to think too hard, but just to make the measurements and move on.

Then in the first student-run lab exercise, they measure angles of refraction in a plastic block with a ray box and protractor.  I go from group to group, cracking the figurative whip.  "Why are you arguing?  Just record the data point and move on."  "Why is there no graph?  No, you're not allowed to 'just graph it later,' graph it now."  "If he's so slow at making the measurement, change roles; you do the measuring, you make the graph."  "You've done fifteen measurements for angles less than 20 degrees.  How 'bout some large angles?" "You've just spent three minutes deciding between 29 degrees and 30 degrees?  Just pick one and be done with it."  

Okay, I freely admit -- *I'm* intimidating the students a bit.  A bit of fear won't hurt.  They're more afraid of me telling them they're doing something silly than they are of the scary lab equipment.  I'm so loud, too, that telling one group something that they can improve means the whole class hears.  Of course, I'm not a jerk here... groups find abundant and loud praise when their data starts looking good.  "Hey, what a great-looking graph!  See what happens when you just take the data quickly?"  I always maintain a smiling face, but I move things along with no tolerance for baloney.

Most of the class figures out by the end of the 90 minute lab period what makes me bark, and what makes me wag my tail.  I hand out candy to the group with the best graph; we deconstruct as a class what we're looking for during a data collection session.  Everyone leaves with a smile, and a bit of relief that loud guy is done shouting.

But then the second week... I don't have to shout at all.

We do the lens experiment shown in the picture above, in which students graph image distance vs. object distance for real images in a converging lens.  For the most part, they don't make the same mistakes they made in the first week; those who do start doing something silly often hear from their classmates before they hear from me.  Data collection is so fast that they're all working on the homework well before the end of the lab period.  

It all starts with weathering the storm in the stressful first lab session.  The same thing worked well in AP physics; so much so, that by mid-year I could just describe the experiment and then sit at my desk while the class got on with their data collection.  

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