Saving Time by Creating Models in Lab

In the summer of 2011, I attended a Modeling Workshop.  It was an intense two week (~90 hours) course designed to introduce us to an interactive method of teaching known as Modeling.  The basic idea of Modeling is this:

  1. Each unit starts with an experiment.  Students collect data and learn how to properly represent and interpret that data.
  2. Students use the experimental data to construct a physical or mathematical model.  For example, a student studying springs might realize that there is a linear relationship between the force applied to a spring and the amount it stretches by, which leads the student to develop an equation as a mathematical model of the relationship.  A student studying atomic bonds might realize that the properties of bonds are similar to the properties of springs, so he or she develops a physical model of an atomic bond as balls connected by a spring.  This is typically followed up by a presentation of results on portable whiteboards (a topic for another post), and the students are asked to come to a consensus on a model that explains their observations.
  3. Students apply the model they created to new situations and evaluate its applicability.

It was an awesome workshop, and it radically changed the way that I teach (by the way, there are Modeling Workshops for other subjects as well).  We were even given a set of materials and a course plan that we could use in our classes.  The only problem for me was that those materials were designed for high school physics, not calculus-based college physics.

In the following year of teaching, I used whiteboards and interactive methods of teaching, but I didn’t exactly follow the Modeling learning cycle as described above.

This summer I decided to spend some time redesigning the course so that I could incorporate more of the Modeling method.  The example lab that I described in a previous post was my first attempt at this, and I recently did this lab with my students.  The lab consisted of taking electric field strength and distance data from a simulation, then plotting that data and using it to create a mathematical model for electric field strength.  After the lab was over, I went back to my office to plan the next day’s lesson.  At first, I just copy-and-pasted the lesson that I used when I last taught the course; the lesson involved using a gravitational analogy as a means of deriving the relationship between electric field strength and distance.  I was pretty happy with how that lesson went last time, as the students got to start with something that was comfortable to them and create something new from it.  Having the students derive it also meant that they didn’t just have to watch me do it.  Lesson done…time for lunch!

Later that day I realized something: we had already derived the relationship between electric field and distance in the lab!  Sure, the gravitational analogy is cool and all, but why waste time doing a derivation when the empirical results had already done that for us in the lab?  Creating the model in the lab had actually saved us a bunch of time…time that I will gladly use on more interesting things in the future.

It makes so much sense when I think about it now.  We generally use regular class time to develop our physical and/or mathematical models, then use lab time to “prove” that those ideas were correct.  In addition to other reasons I dislike those kinds of labs, they are not a valuable use of time. Using lab time to develop those very same models, though, means that we don’t need to spend regular class time on them.  Instead, we can use our regular class time to practice using the concepts that they have learned.

The trick now is to see if I can come up with modeling-style labs for the other chapters we need to cover.


Closing the Gender Gap in Physics Classes

Tomorrow is my first day of class, and I am going to be trying an exercise that is designed to help reduce gender differences in test scores.  Apparently, all it takes is a 15-minute writing exercise in which the students write about their personal values.  More details can be found here.

The human brain is fascinating.

Designing Labs

I hated doing labs as an undergraduate.  I just wanted to finish as fast as possible, and I would take care of the thinking part later.  In retrospect, I suppose that this was mostly because I was a typical sleep-deprived college student, and labs were usually an exercise in tedium.  Everything that I had to do was laid out before me, and all that was required of me was to follow the steps.  The whole process reminds me a lot of this:


I have used boxed recipes to great effect in the past.  This recipe will in fact produce a super moist chocolate cake.  Will it turn me into a good baker, though?  Doubtful.  After repeating many cake recipes many times over, I will probably start to get an idea of the proper ratios of flour, milk, eggs, baking powder, etc., but what if I am out of eggs and need a substitute?

I believe that my duty as a science teacher is not to tell science to my students, but to show them what it is like to be a scientist.  How many of you scientists out there have ever been given the exact steps needed to solve a problem?  The idea sounds silly, yet that is exactly what we do with our students.  Worse yet, we often tell them the answer that they should get (i.e. the “accepted” value for the acceleration due to gravity is 9.8 m/s2), and then ask the students how close they got.  To me, this sends the message that not only is science merely a process of steps that they need to follow, but also that science is already done.

I want my students to feel like they are part of the scientific process.  I want to present them with a challenge for which they must devise their own solution process.  I want my students to feel like their results are meaningful (not inferior because they didn’t get the “accepted” value).  Now, I’m not going to leave the students completely out to dry; clearly, some experiments are complicated enough that some guidance is necessary.  But I believe that some struggle is good.  In fact, an international survey of teaching techniques showed that the countries with the highest math and science achievement allow their students to struggle instead of telling them the steps they need to know (see Michael Pershan’s What if Khan Academy was made in Japan?).

So this is what I want to try this term: each lab handout will consist of a short statement outlining the goal of the lab, and I will also list the materials that are available to them.  That’s it.  If necessary, I will provide some ideas, but I think at the very least students should have control over the number of measurements they make, what particular values they use, etc.  Here is an example:

Goal: Determine the relationship between electric field strength and distance from a charged particle.  (That is physics speak for “Construct an equation that has electric field strength and distance as the only two variables”.)  Your measurements and final equation should include units and uncertainties.

Materials: You will use a simulation applet that you can find at  Data entry and analysis will be done using a program called LinReg.

I’m interested to see what the students think of this style of lab.  I have experimented with it before when I asked students to determine the relationship between drag force and speed for a falling coffee filter, and they really seemed to like the freedom that they had.  My hope is that by doing this kind of lab repeatedly, my students will get better at the process of designing an experiment and interpreting the results.