Southwest Michigan Modeling Workshop Day 7

Knowing that we had done a Unit 4 Balanced Forces intro the previous day, we had the participants read Unit 1 from Camp and Clement as well as Mistrell's article on the "At Rest Condition".  

One of the participants remarked that he really liked how what we read at night related to what we had done that day in class.  No kidding!  Its not like we're just making this up as we go along - although it might seem like that sometimes.  Doing the reading without the appropriate context would be as meaningless at lecturing about inquiry teaching.  So we try to make sure that anything they read is meaningful.  

I told a story about hearing an elementary school teacher at the MSTA conference tell everyone in the room that "Gravity was the force of the air pushing the ball down".  They were shocked!

I also told the "Heavy Boots" story; but in the first person.  I do that occasionally because telling stories in the first person sometimes makes them more believable.  

I really like telling stories in class (and in the workshop).  I think that I do it because it is fun.  I am not under any delusion that these stories are advanced pedagogy.  But having a little fun in class can be fun.  And there are times when students have come back after years and that story is what they remember.  I hope that they remember the associated concepts too but...

As for the Camp and Clement reading, the participants really seemed to like it because it is almost an instruction manual that they can use to attack the misconceptions associated with the "normal" force.  I am not a huge fan because it is a little too prescriptive for me, but that is a 14 years veteran opinion.  I think that as a new modeler or a young teacher the book "Preconceptions in Mechanics" would be invaluable!

It is amazing how so many physics teachers' students struggle with the "normal" force - actually it is not amazing how many students struggle.  What is amazing is how many teacher are frustrated and don't do anything about it!  It may be that the just don't know what to do or that they blame the students for not paying close enough attention.  Either way it is a difficult topic that really needs coherent concept development.  Camp and Clement can help with that!

The participants then embarked on worksheets 2 and 3.  To get them going we developed, as a group, some problem solving steps:
1. Draw the system schema
2. Draw the force diagram 
3. Resolve any diagonal arrows into the "shadow arrows" also known as the components
4. Apply the numbers to the arrows and solve

The participants put some of these on white boards and Laura facilitated a board meeting.

This is where things got weird.  It was Friday afternoon of a full week of the workshop.  Everyone was tired, some were sick, one had one eye available.  And then we asked them to do a couple of problems from unit 4 worksheet 5.

This worksheet is really where the rubber meets the road; separates the men from the boys, is legitimately challenging for even seasoned, veteran physics teachers.  The questions show two boxes being pushed by a hand.  The first question is, "which pushes harder, A on B or B on A?"  Then they were asked to draw force diagrams for the situations.  

This is not obvious for students nor novice physics teachers.  The FCI is rife with these questions!  And I know that this is a misconception that persists.  I noticed by walking around that many of the teachers easily put A on B = B on A but their force diagrams didn't really represent that idea.  

There was obviously a disconnect between "knowing the rule" and really understanding how these work.  

We didn't really look at these as a group - the facilitators walked around and engaged the participants in dialogue while they drew their diagrams and schema.

To answer the questions we set up for them some dual range force sensors (thanks Vernier) on some carts and had the students reenact the situations.  They pushed and pulled with the same and then different masses.  They they rammed them together!  

No matter what they did the forces that each exerted on the other were always the same!

We asked them to see if that result matched or contradicted their diagrams.  Most thought this matched what they had but had to modify their force diagrams to compensate.  

One very interesting interaction involved a participant that said to me, "when we started I put that the forces were equal.  Then we did the worksheet and I want to change it to B was bigger.  Then we did the lab and now I want to change it back to equal.  I really don't think that even though I knew the rule I totally understood how it worked."  

This type of cognitive conflict is exactly what we're looking for!

The last participant interaction - which I thought was very valuable - happened with at the end of the day.  She was really reeling from the worksheet and the lab and asked, "I wish we could just set it up like it is on the worksheet and see the forces."  So I grabbed a third force sensor and we did just that.  When we ran it she said, "Look, it is bigger!" referring to the pushing force compared to the interaction forces.  

You can't pay money for that moment - where the new concept is cemented in their brains by a concrete experience.