Monday, June 30, 2014

Sum of the Forces - what's a sigma?

My co-facilitator and I were having a conversation on Thursday about how we wanted to attach the forces unit on Friday.  I asked her where she went with her own students from here and she described the 5 step problem solving process.  I asked her to describe it for me and she told me this:
1. Draw the system schema
2. Draw the force diagram
3. Resolve any diagonal forces into the components
4. Write the sum of the forces statements (with a sigma)
5. Solve the problem

I thought about this all Thursday night and was very conflicted.  

I love 4 out of the 5 steps...but couldn't get on board with sum of the forces statements.  

Why?

My thought is this - if we have the participants write sigma F statements it looks WAY too much like something that they have already done or something you'd find in a text book.

I want this (the modeling method) to look vastly different to the participants so that they aren't relying on some traditional mode of instruction.

I am afraid that some participants will take this and think it is an addition to what they already do.  Like, "when I teach the students about normal forces I'll make sure to do these worksheets."  This method is not something you do in addition to your lectures!  

In addition, when our procedures are different it puts the participants in a place to question why they have done things the way they were doing them before.  Is it the way you were taught and/or the way you've always done it.  

The real question is, how do you get students to develop their own process and procedures?  

Telling them to write sigma F statements won't really help.  So I suggested to Laura that we just take it out and see what happens.  To my delight there seemed not to be a real problem.  In fact, the participants were writing mathematical statements that were very grounded in their force diagrams.  They were setting forces equal to each other based on the diagram and solving from there.

I was elated.

So I love the 4 steps - and I'll be bringing it to my students in the future.  And I am so glad we thought deeply about the sigma F statements and were able to make modifications that are positive for the participants.


1 comment:

Don Pata said...


OMG! Steve - you brought these to my attention a couple of years ago but I didn't see how they could enhance student understanding. At the time I thought they would actually work against me in that they seemed more abstract than the force diagrams themselves.

After working with a teacher who has been using them for years (since 1998) I realize that they are a precursor to a force diagram!

They do show the N3LFP very well but in addition we can apply the first rule of forces in that every circle must contain a physical object!

I have never used them with my students but I'm going to this year.

I'll let you know how it goes and you'd better believe I'm going to show them at a modeling follow up and a DMAPT!