Sunday, September 7, 2014

Having a Ball with Chemistry

We're nearing the end of Unit 1 in my classroom, so it's time to start thinking about the summative assessment.  To prepare my students for the tough problem they will face on that test, I need to give them some monster problem practice opportunities.  For years, I used the chemistry standard "find the thickness of aluminum foil" for this.  It's a great problem because the students have to use the combined concepts of density and unit conversion to find the thickness (thinness?) of a square of foil.   

The trouble with that assignment is:  who cares?  Most students don't have a burning question about the thickness of aluminum foil.  They'll do it because I ask them to, and they might become better problem solvers, but it always felt kind of "meh" to me.  Taking a cue from one of my favorite thinkers and bloggers, Dan Meyer (his blog is included in my reading list at the right), I made this video.  OK, disclaimer:  it's not great, but it is a first attempt (and it's another video made with my Lumens Ladibug document camera - I can't get enough of that thing):

So then I pose the question:  Will a bowling ball sink or float in water?  Cue the eyeroll.  OK, I admit that this one starts out in sort of the same way as the foil.  The question is maybe not burning here either, but they are talking about how crazy it is to even ask that question as they work together in lab groups to solve the problem.  And that's where the fun starts.  There are three bowling balls, two groups solving for each ball.  Good conversation about unit conversion and density as I circulate.  Kids talking about the merit of measuring in centimeters vs inches, the difference between mass and weight.  When they finish the problem about 20 minutes later, we reconvene as a big group to make predictions and test them out.

I made a video of that too.  What I wish I had videotaped was the reactions of the students as we did it.  In every class, there is a group of students who doubts that there math is correct.  They check and recheck their figures.  In one group on Friday, an friendly argument erupted where finally they had to agree to disagree because one very strong student was so convinced that she had calculated it wrong.  We test the green 15 lb and black 10 lb bowling balls first.  Kids correctly predict that they will sink.  Then we test the purple 8 lb ball and kids cringe and shrug as they guess that it won't sink.  Video #2:

And then they cheer.  Literally cheer and high five like they have won a game as they see the results.  No one ever cheered after aluminum foil.


  1. All done well, but bowling balls are expensive. Where did you get yours?

    1. I used to go to an alley and borrow the 8 lb ball. Two different alleys always let me borrow. I steal the 10 lb and 15 lb from the physics teachers. Then one year I out it out to the staff and parents at open house that I needed a lightweight bowling ball. People are always happy to give away things that they no longer need. Someone donated an 8 lb ball.