# 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

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

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.