Thursday, July 24, 2014

Southwest Michigan Modeling Workshop Day 13

Today started with one of the most important readings that we will do this summer - the Swackhammer article called Making Work Work .  This is an article that Swackhammer started in the late 90s and finished in the early 2000s.  I got a hold of it when I was at ASU in 2005 and is all about ENERGY!

The research into student conceptions of force and motion has been ongoing since about 1980.  However, research into the energy conceptions has only been going since the late 90s.  So the research is pretty recent (by the workshop standards).   Swackhammer posits that energy is just energy and that the only thing that differs is where/how it is stored.  Calling energies with different storage mechanisms different "forms" leads to the idea that they are fundamentally different.  In addition, the idea that work can be defined by an equation divorces is from its conceptual meaning.

Normally I would have thought there would be a participant uprising (last year there was almost a fistfight) but the participants were more like, "Yep - that makes total sense" which means that the brainwashing we've been attempting for the past 4 weeks has been successful. :)

They liked the bar charts in both the Swackhammer article and in the Van Huevelen article  Multiple Representations of the Work Energy Process.  This was a bit older than the Swackhammer article but the participants still got a lot out of it.  They really liked the bar charts which is good because we used them a lot later.  They didn't, however, like the usage of the term "potential" energy.  And neither do I.

If all energy is stored somehow and knowing where / how it is stored then what exactly is potential energy?  Just calling it that doesn't help us understand where / how it is stored.  And actually it makes is sound like it is not actually energy but is is "potentially energy".  I say:


I know that that is a pipe dream - we'd have to change every physics text book forever but really, if we're going to be as explicit as possible with our language to promote actual student understanding why wouldn't we change?

After the readings we had the participants facilitate the white boards for the pie charts worksheet we did the previous day.  This is always an adventure because that particular worksheet is super vague and there are a ton of correct - but different answers.

One of the things I tried to do this year - and failed badly - was to give the participants as much practice and guidance in facilitation as possible.  The problem is that facilitation is very hard and because I've been working on it for 14 years, I make it look kind of easy.  However, I do not know exactly what I do or how to do it.  This was a strength of the woman with whom I taught the previous 4 years of the workshop but this year I have sucked at conveying the "what" and the "how".

Nonetheless, the practice is still important and the "student modes" of the participants is getting really good.  There was a ton of good discussion of the pie charts and it prepared us for the bar charts.

One of the long discussions that we had was, where does the energy go during sliding and/or during a collision?  I did a favorite demo where I had them crash two 2-inch steel spheres together with a piece of paper between them.

Both of the articles showed energy transfer and conservation through bar charts.  I asked the question, "Why are these better and worse than pie charts?"  This sparked a bit of discussion and from there I did a bit of direct instruction on how I think bar charts should be constructed.  From there I set them to work on unit 7 worksheet 3a.

When they were finished we broke them up into two groups and had them facilitate some white board discussion.  Again, I would have loved to give some insight into how to do this better but just let them practice blind.  I'm going to have to work on that for next year.

This is when things got interesting.  I had one of the participants stretch a spring and asked how it felt.  My question, "What, if any relationship exists between the stretch distance and the force by the spring?"  At this point we are very well versed in the inquiry lab procedure so they pushed through it very quickly.  They made white boards and we asked the question, "How are they the same and how are they different?"

The participants notices that all of the graphs were linear and that the slopes were all different.  This lead to a conversation as to why they were different - and they defined the slope as the spring constant as a measure of the tightness of the spring.  Cool.  We used their equations to develop the general idea F=kx.

This is where the "hand waving" begins.  I asked them to look back at their white boards.  My question was, "When we stretched the springs, were we storing energy in the spring?"  Their answer was, of course, yes.  "So then where is this energy on your graphs?"

This is a rather obscure question but one that needs answering.  The reason I don't like it is because no participant or student would ever come up with it themselves.  This the hand waving.  Because they are stumped by the question I ask a follow up.

"When we look at a graph what are the key components that we're examining?"  They listed:
1. The values of the points themselves and trends in the data
2. The slope
3. The intercept
4. The area

If these are the things that we look for on the graphs are any of these the energy?  Because we already examined 1-3 on our list, we were left with #4 and we defined that as our energy!  I had them write an equation for it and substitute in the F=kx from above and presto we have our first energy equation.

I don't love pushing them into this definition of energy: the area under a force distance graph, but its all I've got now.  In my 15 years of practice I haven't come up with or seen anything I like better so for now we'll stick with this.

The participants were fired up (in a good way)!  From many of them I heard, "I knew that equation but never knew where it came from!"  I love that.

Where to go from here?  I set up two clamps at the end of a lab table with a track between them.  I stretched a rubber band between the clamps, over the track, so that they could pull the cart back against the string and if they let it go the cart would zoom down the track.

The question is, "What, if any relationship, exists between the energy stored in the string and the speed of the cart on the track?"  There was some discussion of how to find the energy stored in the stretchy string but in the end they were able to graph the relationship.

Long Day!

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