# Day 128: Back At It

Spring Break in Neenah has come and gone… now it’s the final push to the end of the year.  I always get mixed feelings after spring break.  Panic… sooo much yet to cover (well to learn); Pride– all the students (well most, … no all) have grown so much and are much better (physics) students than they realize; Sadness… this group of students will be moving on, that’s sad (for the most part); Frustration… I still have not figured out how to reach a few students. No matter what I try, it just does not seem to work.

Today was to be the day we had the post – lab discussion for the collisions experiment we started on the Thursday before the spring break.  It seems to be taking longer this year.  I did a few new things this time around.  Each group shot a quick movie of collisions they studied.  Here is an example:

And one more.

I also required the students to use a spreadsheet (or Logger pro with calculated columns) to complete all the calculations. All of the data will be pooled and dumped into one Logger pro file to create a graph of total initial momentum vs. total final momentum.  If the slope turns out to be equal to 1.0, then we know that momentum is conserved.  The new part for me was setting up a google spreadsheet for the (CAPP) students that were required to complete the analysis of a 2D collision using our hover pucks or our air hockey table.  I’m a bit ashamed to admit it, but this is the first time I have used a google spreadsheet with my classes.  It is awesome to sit and watch the data get entered.  Hopefully we will be able to see momentum conserved in both the x and the y directions.  I will probably not go into any detail about the center of mass of a system aspect unless the opportunity presents itself.  In my experience, conserving momentum in two separate directions.

SIDEBAR:  In my mind I am wrestling with my sequence.  I have been teaching momentum( and impulse) AFTER Energy and dynamics.  As of late, though I have read more about teaching momentum (and impulse) BEFORE energy and even before some aspect of dynamics.  I’m just not sure if there is a pedagogical advantage one way or the other.

General Physics:

Today we discussed the Energy bar chart (LOL’s) assessment they took the day before we went on break.  We also had the pre-lab discussion for the Hooke’s Law experiment.  I do not do the traditional Hooke’s Law Experiment with masses being hung on a vertical spring.  I phrase the purpose to include something like this:….  determine the relationship between the force exerted on a spring and the change in length of the spring.  I find it makes it easier for the students to transition to a compression spring because the ‘change in length’ could be a ‘get longer change in length’ (like our extension springs) or a ‘get shorter change in length (like a compression spring that will be used with the Pasco cart launchers). Here is a picture of how the data is gathered:

The spring are pulled horizontally so there is no confusion about any gravitational affects.  This also makes it much easier to transition to the compression spring and determine it’s spring constant.  Each group did two springs to see that the slope of the linear graph does depend on the spring AND to have its data confirmed.

# Day 127: Collisions and LOL’s

Today was all about gathering data for the collisions experiment.  We did not get finished so tomorrow we will wrap up data gathering and the analysis.  It’ll be a chance to have some of the students learn how powerful and useful spreadsheets can be.  I’m also having them post a movie or three of the collisions to our Schoology site so we can reference them during our discussion AND so I can send an email to the parents to let them see what their sons/daughters are up to in physics.  I wish I had remembered to post a Tweet about it earlier today.

General Physics:

Today we WB’ed the Energy Bar Graphs (aka LOL’s).  I really like WB’ing this because it provides a chance for some really rich discussion.  Here is an example:

After we agreed on the analysis for this problem, I made an addition to the problem:

I added a second path and asked from which path, if either, would the crate have a greater velocity when it reached the location marked by the arrow. We discussed it and most agreed it was the same…. but thankfully, some students needed proof.  I used this:

along with a Bee-Spy photogate to prove that the velocity was the same.  Yep, it was a pretty good day.

# 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.