Days 125 and 126: Two for the price of one (Wealth and Momentum)

Well, it is two post tonight because I was sick last night… massive head cold tried to take me out… it did not succeed!

Day 125

Advanced Physics

The students completed the ‘Forces Diagnostic’ for the second time, the post test.  I have not analyzed the results yet with the awesome spreadsheet, but I did have several (maybe 3) students with perfect scores of 30 (and a bunch with 29’s), none of them had nearly that high on the pre-test.  We also discussed the one problem from the COE test they finished the day before.

General Physics:

So I was NOT FEELING WELL by this time, my Mod 4 class was (in my mind) awful.  I did more telling than asking.  The topic was connecting the Jewels activity to the new topic — energy using the wealth analogy.  I know I mentioned this when writing about the wealth analogy when the advanced class did it, but I LOVE this analogy… so easy for students to identify with.

During my prep hour I decided to swap my approach for the next class.  Rather than TELL the students we are connecting to energy first, then introduce the wealth analogy… I went right from summarizing the ‘data’ from the Jewels to the wealth analogy. I knew this was what I wanted to do, and you know how sometimes a student will say or ask just the right thing at the right time, well it happened here.  The perfect segue.

I asked what it meant if you had earned a lot of jewels and they had been real jewels?  A student replied they would be rich… or wealthy.. bingo, I’m off and running.  During the discussion, the right words and phrasing just came to me.  I wish I had recorded it, everything flowed just perfectly.  The kids were engaged in the discussion… it was awesome.  The last step was to connect it to energy. To get there, I reminded them that our definition of wealth was a quantity that could change one’s life, well getting back to physics, there is a quantity that is capable of causing a change in a system.  The name of that quantity is energy and then we’re off using all the bits from the wealth analogy to build energy concepts.

So even though I felt like absolute shit, the class was really a good one… I went home and went to bed early.

Day 126

Advanced Physics:

Today was the first day of our momentum unit.  I developed the concept of momentum using an approach I modified from one that Frank Noschese wrote about in his blog post “Inventing Momentum”.  Unfortunately, I could not find the link. The progression using colliding dynamics carts to build the idea of a v-m bar graph, and that the area trapped by the v-m bar is meaningful… we define it as momentum.  He then goes on to explain that momentum is conserved, but challenges the kids to try to come up with a situation (using simulations) to show when it is not conserved… of course they can’t.

I like this progression because it naturally build a pictorial representation for momentum that is especially useful for answering conceptual questions.  I stray from his approach asking the students if they think the trapped areas should be the same.  Sometimes I get lucky and a student will ask,  then I respond by asking how would you test it… now we have a purpose for the collisions experiment.

When we do this experiment, I break the class into four larger groups.  One group will look at six different inelastic collisions (so two smaller groups do 3 each), same thing for elastic collisions, and for explosions.  The last group is my CAPP group, they use our air hockey table (and/or hover pucks) to do 2D collisions.

Tomorrow is about finalizing what the parameters of each collision will be and gathering data.

General Physics:

Today we used our energy blocks to analyze a bunch of situations.  Here is a set of energy blocks:


We use them two ways.  First, I gave them a situation, For example, a basketball held at rest above the ground… what energy asset and how much?  Then move it higher, now how much, then change it to a basketball… or a dynamics cart rolling on a track.

The second way is to give them an initial situation (a spring-loaded Jump-up toy poised to, well jump up) and a final situation (the toy half-way to its maximum height).  The students use two sets to depict the energy distribution.  In a concrete way, they are constructing energy bar charts.


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