NGSS Using Models Resource

In thinking about models and using models in my teaching, I found this helpful source at Bozeman Science on Using Models

 This short video helped clarify my thoughts on the difference between mental models and physical conceptual models.

Just as when you buy a new car, say a green Toyota Prius, you start seeing green Toyota Priuses everywhere, I am now much more conscious of how often we use models.  In teaching the GEMS guide, Secret Formulas, the toothpaste is a favorite. Using the ceramic floor tiles as a model for stained teeth is an example of a model that does not resemble a tooth very much, yet it effectively models enough of the cleaning to help students understand the need for both some form of soap and some form of mild abrasive.

In a PK unit on fungi, I realized the picture book we read, demonstrated the differences between plants and fungi, as well showing example of many of the scads of species of fungi.  The pictures in the book were two-dimensional color models of the real object.  The color and label outline diagrams of a mushroom help model the structure and function of the mushroom.

This all helped me realize that in teaching a concept, such as "mushroom", it is very helpful to use a physical conceptual model that  is visible and shared by all, rather than just referring to an abstract image.  When I show a picture or hold up a physical model, we all see the same thing, whereas if I just refer to "those little white umbrella shaped plant-like things that pop up after a rain" there is much more room for misunderstanding.

Making Toothpaste is Easy, Modeling Decay Bacteria Harder

For the last several years, we’ve made toothpaste with my class and they’ve always had fun doing it.  Part of the excitement comes from the idea that they are actually making something that is usually bought in a store.  It is cool to show them how to make things they are familiar with, but never thought about doing themselves.  I call it the Chemistry of Everyday Things – which always reminds me of Don Norman’s classic of cognitive science, The Psychology of Everyday Things.  The GEMS guide Secret Formulas from Lawrence Hall of Science has projects making paste, a cola-like beverage, and ice cream, as well as toothpaste.  As always, I change the basic activity around to tune it for my class and whatever seems interesting that year.

When asking them about what was the basic purpose of toothpaste, I’m sometimes surprised when it takes several responses before getting to “cleaning our teeth.”  Modern marketing is doing wonders with selling taste, tooth whitening, colored gels, and stripes.  This year just before we started on our toothpaste project, I had just been re-reading the section on mouth bacteria and tooth decay from Natalie Angier’s The Canon: A Whirligig Tour of the Beautiful Basics of Science and was captivated by her description of over 600 species of bacteria at work in our mouth to cause cavities.  After some more background reading, I felt I needed to do more with helping them get a better picture of the massive ecosystem at work in our mouths.  Just telling never works well, so I started looking for some kind of model to illustrate.   

My first thought was that some teacher must have made a good quality, scientifically accurate video that was hopefully a bit less terrifying than Texas Chainsaw Massacre.  But I didn’t find what I wanted.  There were lots videos of dentists in white coats just talking about film on teeth.  Also, there were lots of really gross videos and photos of mouths of rotting teeth.  One video intended for college students had fascinating content about how the various bacteria had different functions and how they communicated with each other.  Unfortunately, the animation was too abstract and the content level and the cognitive load were too much for elementary students. 

I’ve started thinking about getting a model tooth, like the ones in the dentist videos, and seeing if I can find a way for something more or less like bacteria to grow on it fairly easily and quickly.  Or alternatively, to find some kind of highly visible coloring or film we could brush off as a way to model the growth of bacteria. 

Physics Models and Physical Modeling:

This fall we have been working on the FOSS unit Mass Force and Models.  We began with the Pendulum module and the investigation covers the basic ideas of variables and what variables affect the frequency of a pendulum.  We made pendulums with string, paperclips, and pennies to test which of three variable might affect the frequency:  mass, release position (amplitude), or pendulum length.  In some sense, these pendulums could be considered as models, as they were not designed as part of a machine, to regulate a clock for example. 

When we tested length, we recorded our data and then hung the pendulums on the wall according to how many cycles they achieved in 15 seconds.  The lengths has been calibrated so that as the hooks, labeled from 5 to 21, increased in ordinal value, the length of the pendulum hanging there decreased, describing a half parabola.  It is really cool to look at and the kids are always amazed by it.  FOSS termed this physical model as a physical graph.  We talked a bit about what the graph shows, about the relationship between the length and the frequency, and then a bit about the underlying math, the parabolic relationship.

As an idea I’d like to see if we can plug the data points into Wolfram’s Alpha and get the equation of the parabola we found experimentally.

Then the students turn this physical model into a 2-D paper model be making what FOSS terms a pictograph, a graph that abstracts a little, but pretty closely resembles the physical wall graph.  From this they see the first step of abstraction.

Then they turn the same data into a 2-coordinate graph.  For many of them, this is one of the first 2-coordinate graphs they have done and just learning the mechanics is a good lesson.  I always insist on them labeling the axes with not only the number lines, but also with the units and the X and Y coordinates, as well as a title.  From here we work with this pretty abstracted model to get more a sense of the underlying physics.

If I can get them a calculator to give the equation, then we’ll have also tied in the Math, moving from the actual pendulum or pendulum model to a physical graph to a pictograph to a 2-coordinate graph to an equation, which is a mathematical model of the pendulum.  This will be pretty neat!

We may also need to build a really big pendulum using weight plates for some to let go of the misconception/alternative conception that while mass makes no difference at lower values of mass, it will certainly alter the frequency of a pendulum at higher values, with really big weights.