Tagged: modeling

“But We Were Told Light is Waves”

It’s amazing what some students have heard and believe on “school faith.”

As the first activity in my Physics 2 class we do the Pinhole Camera with a light bulb and view the image on a screen. The first day I showed the class how to create a simple pinhole camera out of a box and some aluminum foil (if you want to see what mine look like let me know.) This year I rewrote the lab to be totally inquiry based. They made a number of general observations and wrote 7-10 “I wonder…” statements or questions, they then experimented and tested their “I wonder…” statements and made observations. This rewrite to an inquiry lab was great. All of the groups wondered about and tested the same things I had on my previous version of the lab (move the screen, move the bulb, make a bigger hole, make multiple holes, use two bulbs, etc). So that part of this process was excellent.

The next day after a brief discussion about some of the observations we saw I instructed each group to create a model on a WB for the situation. I reminded them that the model should be simple, but yet be able to explain ALL of the observations they made. Here are two of the models I got:

Pinhole Model 1

Student justification: “Light travels in waves”

Pinhole Model 2

“I was told light is a particle that travels in waves.” Thus the dots in wave form here. I find it interesting that the waves keep getting bigger. The student had no particular explanation for that, just that they were waves.

I keep trying to ask “what about this lab shows that light travels in waves?”

“I don’t know, but it does.” was a common response.

It took myself and another student group about 20 minutes to finally convince the bottom group in particular that we don’t need to model the light as waves. And even now I’m not sure if they bought it or just wanted to be done with the conversation so they gave up.

“Why can’t we use straight lines.” another group said. Their board did show a linear model for the light, and they had the arguments to back it up.

“We have no evidence to back up the claim that they are waves.” I said. “Straight lines explain the behavior and it’s a lot simpler to use then draw crazy wave forms.”

I went on to say that “we haven’t “disproven” the idea of light as waves, but we surely haven’t proven it. Science comes with the burden of proof.”

So as I analyze this class discussion a couple of questions come to mind:

1) Do other modeler fight this battle of using a model that we have evidence for vs. what they have been told. (I find it A LOT in chemistry too, especially with the atomic model)

2) Was this a lesson for my students about science at its finest? Did I end the discussion too quickly because I wanted to “keep moving?”

3) Should I let them use their mental model until it totally breaks down and/or becomes too difficult to use?

If you have any answers or thoughts about these questions, please comment below.

Modeling Acids and Bases Lab

As my paradigm lab for Acids and Bases in Chemistry 2 we do a very simple classifying lab.  My lab handout is here: Classifying Lab

Basically what this entails is that I give the students 7 substances.  HCl, H2SO4, HNO3, NaOH, KOH, Ba(OH)2, and H2O.  They know the formulas and proper names, but NOT acid names (i.e. Nitric Acid).  I have each group do some qualitative tests in well plates using various indicators and other chemicals.  They take observation data in the table provided.

After all test are complete the students are to group the 7 substances into as many or few categories as they need.  They just need to justify their groupings.  After a little staring at the data most lab groups are able to see the pattern that emerges.  They almost always create 3 groups.  One contains HCl, H2SO4, HNO3, One has NaOH, KOH, Ba(OH) and H2O is by itself.

During our whiteboard discussion each group explains their reasons for putting certain things together.  Sometimes they talk about only one indicator but most groups see the patterns emerge across all the tests.  After we have an agreed upon grouping system I then pose the question, “Now look at your groups what do each of the substances have in common within a group?”  Obviously you always get a variety of answers but the initial responses usually revolve around how one group has begins with Hydrogen and the other ends with Hydrogen.  I remind them about what is significant about the order compounds are written in, and also what is significant about the Conductivity test we did.  They realize we are dealing with ionic compounds, and the first ion is positive, while the second is negative.  They also see the Hydrogen “on the end” always comes with an Oxygen, and we have hydroxide.  Someone usually also realizes that water is really just HOH, thus a combination of both of these groups.

My class this year is quite bright and it didn’t take them long to verbalize these patterns.  Within only a couple of seconds of this “light bulb” going off one young lady exclaimed.  “Can we make this a Vin diagram!?”  “Why not?” I said, “that would be a great way to model this!”

How perfect!  Never a mention of the words Acid or Base, and we have Arrhenius’s Model!  Concept before name!

Naturally the next day I challenged them by testing NH3.

To which a young man exclaimed.  “Here we go again, we create a Model one day, and the next day we prove it wrong!”

I said, “Don’t shoot the messenger, that’s the way the world works.”

He then added, “in English they call it an exception to the rule, but in Science we create a new rule!  That is why science rocks!”

Holy cow, have I done my job here?  At least it made me feel good that I’m getting through to a few kids!

Physics Week 1 – Circles Lab

Last week was our first week with students for the school year.  For the first time (I think ever) I’m actually quite pleased with how my classes went.  This post will outline my week in Physics I class.

Physics I is class that consists of Juniors and Seniors.  All have taken Science 9 (mostly physical, but other as well) and 10th grade biology, some were in Chemistry last year but not all.  Mathematically the range is from Algebra 2 to Trigonometry to Pre-Calculus.

This year I’m trying Unit packets (i.e. Kelly O’Shea), so on Day 1 I handed out my Unit 0 Packet.  More on Unit 0 later.  Using a packet will free students from individual Lab Notebooks and hopefully guide them to focus on lab content rather than organization.  The strategy allowed me to by pass all the Lab Notebook setup stuff I’ve done in the past.  So I was able to just get started.

I began with a circle drawn on the board.  My first question was, “How could you describe this shape, WITHOUT using the word circle.”  Things such as ’round,’ ‘curved,’ ‘360 degrees,’ ‘all points equidistant from the center,’ were stated.  Good enough.

Since I introduced this lab as and exercise in measuring I next ask the students what could we measure about the circle.  The usual things were brought up: radius, diameter, circumference, area, and maybe something else.  Next I said we needed to narrow our list down to the two easiest things to measure.  We agreed upon circumference and diameter.  I have a classroom set of 10 meter tape measures, so from there I let them go.

I made sure to emphasize that this lab was a MEASUREMENT lab, because a few students always try to get away with calculating circumference.  One thing I did not mention was whether to measure in inches or centimeters.  I got about a half and half return.  I set students free to find circles around the school building, with the goal of measuring between 10 and 12.  This takes about 30 minutes.

The next day the students returned to class with all of their measurements.  From there it is time to graph.  In the past I’ve gone directly to LoggerPro, but this year I decided it was important to at least draw a couple of graphs by hand.  I gave them the following guidelines:

One your Graphs be sure to:

  • Use Pencil
  • Label your axes with symbols and units
  • Give the graph a title (“[vertical axis variable] vs. [horizontal axis variable]”)
  • If the data is linear, draw a Linear Fit line (don’t connect the dots)
  • Find the slope of the line using points on the line (not data points)
  • Write the equation of the line (EOL) using the variables from your axes (not “x” and “y”); make sure the slope and intercept have the correct units attached to the numbers.
  • Put units on numbers, but never on variables

I did NOT tell them which axis which variable need to be on.  I again got about a half and half return, which is good for the whtieboard discussion.  I did have to do some “teacher talk” regarding the Linear Fit line and the EOL.  Since these are things that we will be doing ALL THE TIME I feel it was important to spend a few extra minutes to introduce common terminology and expectations.  Hopefully it makes my life easier in the future.

Once graphs are drawn by hand on paper each group transfers their graph to a whiteboard.  It doesn’t need to be a perfect graph, but something that shows approximate locations of data points, and most importantly the Linear Fit line and the EOL.

The final piece to the puzzle is the whiteboard discussion.  We take our time presenting and discussing things such as methods of measurement, variety of sizes measured, why they decided to put C and D on the axis they did, how they calculated slope, etc.  We then compared all groups graphs to each other.

The first thing that was noticed by the students was that graphs that were C vs. D were different than D vs. C.  GOOD!  Then they realized that the graphs that were done the same all had slopes that were very close to each other.

Me: INTERESTING, why would that be?
Students:  Because we all measured circles.
M: Oh, ok, so what does this slope  mean then (looking at the C vs. D graph)?
S:  Well they are all around 3.
M: Exactly 3?
S:  No, just a bit more.
M: Interesting
S: Pi
M: Who had pie?  I like pie.
S: No the slope is pi.
M: Cool, what about this one?  (D vs. C graph)
S: Inverse of pi
M: What does that mean?
S: 1 over pi
M: Why?
S: The variables are graphed on the opposite axes.

Ok, you get the idea, but more importantly SO DID MY STUDENTS!

Based on all of this discussion we are now able to write and mathematical model for circles.  From the C vs. D graph we get C = πD.  From the D vs. C graph we obtain D = (1/π)C.  Someone usually notices that these models are one in the same.  This is awesome, because most students realize they have seen these equations before in some form or another, but never had the experience of knowing where they come from.  Thus I give them one of my favorite sayings: “Equations come from experiments NOT textbooks!”

The very last thing I added this year was a quality addition.  I took time the next day to do a summary of  how models were used in this lab.  On the whiteboard I created a summary that looks like this:

The final thing I wanted to do was come up with a definition for the term Model.  With a little guidance both of my classes agreed on the fact that a MODEL IS A REPRESENTATION.  I can now refer to this simple definition anytime students wonder what the heck I’m talking about when I call and equation a model.  It simply represents the situation in a mathematical form.

I absolutely love the way this lab introduces my students to just about everything we are going to do in physics this year.  Defiantly worth the 3+ days to complete.

WOW!  How can something as simple as measuring circles turn into this ridiculously long post?

My Modeling Story

When I finished my undergraduate studies in 2004 I had no knowledge of Modeling instruction.  I began teaching my science classes in an interactive, but very traditional way.  It didn’t take me long to realize there must be a better way.  As with most of us, I consider year one as a mulligan, I survived, and that is about it.  During that time I was employed at Brillion High School in East Central Wisconsin.  My assignment was mainly Freshmen Physical Science.  During that first year, a colleague of mine, Ryan Peterson, invited me to the local Physics/Physical Science share group meeting where I meet Scott Hertting, Dale Basler, Greg Franzen, Jeff Elmer, and many others who were talking about this Modeling thing.

My interest was sparked!  Those guys had so many awesome ideas and seemed so passionate about the way they taught, it was contagious.  I continued to struggle through year one, and finally it was over.  The next school year I was given the responsibility to teach physics along with physical science.  Scott Hertting was gracious enough to meet with before  school started that year and shared almost all of his materials with me, and explained even more about Modeling.  After blindly learning as I went I could see the effectiveness of Modeling, despite my own short comings.

It was in the spring of 2007 when I received my first formal Modeling training when I took a class at UW-Oshkosh with professor Mark Lattery.  One summer later (2008) UW-Oshkosh began its MSE C&I program in physics.  For the next three summers I studied the “ins and outs” of the Modeling Method from some of the best teachers around.  Included in the Masters program was an Action Research project.  Two other teachers and I studied the effects of “Grading Discussions in a Modeling Physics Classroom.”  In 2010 I earned my Masters of C&I in Physics.

During the summer of 2008, in between my Masters studies, my career took me to a new school with a new teaching assignment.  Bloomer High School hired me as their new Chemistry and Physics teacher.  It was at that time when I began to explore the Modeling Chemistry curriculum, and have never looked back since.  My current class schedule consists of Chemistry I and II, and Physics I and II.  All 4 classes I have designed to use Modeling Instruction.

Future posts will describe each of my classes and how Modeling fits into each.