I sat down to grade the second midterm for our Introductory Algebra-based Physics course. Exam grading can be simultaneously rewarding and punishing; you get to see exactly how much your students have improved (or not) in their abilities to solve physics problems. It was during this grading session that I had an epiphany about story problems and the ways many students struggle with them.

The problem in question states:

A box slides up a rough, wooden ramp and comes to a stop. Below is the free-body diagram for the box while it slides up the ramp.  Does the free-body diagram match the description of the situation?  Explain your reasoning.

Many students correctly identified that the acceleration (net force) along the ramp is wrong as it needs to be pointing down the ramp in order for the block to come to a stop. Some students also correctly identified that the normal force drawn on the FBD is longer than it should be (forces must balance perpendicular to the ramp where acceleration is zero).

All but a small handful, however, missed the fact that the FBD included a force pushing the block up the ramp even though no other objects or forces are mentioned in the story problem. Many students say something like “the force pushing the block up the ramp” or “the tension force pulling the block up the ramp” even though neither pushing nor pulling were described in the problem statement. The bigger issue is that another common statement associated this force with the velocity: “the force pushing the block up the ramp is correct, because without it, the block would not be moving.” At first glance this statement makes me think students are (incorrectly) associating force with velocity. On the other hand, the statement is fundamentally true: the block would not be moving up the ramp if there had never been a force acting on it. The issue is that we wrote the problem assuming that force had already gone away and that the block had some velocity up the ramp. The students know intuitively that blocks don’t just move spontaneously up ramps; did they just assume the force was still there? Hence my epiphany:

Story problems are hard because physicists are excellent problem solvers, but not always excellent storytellers.

These students needed the backstory behind this situation. What is the block’s motivation? Why is it moving up the ramp? Without that information, they are perfectly comfortable including a force that should (in our minds) not be there. In the literary sense, that force was implied by the fact that the block is moving up the ramp. As we emphasize in the liberal arts, every discipline relies on the others. For this very reason it is important that we recognize students will answer questions incorrectly for a variety of reasons: sometimes the reason is that they haven’t mastered physics… but, at least occasionally, it is also because we haven’t mastered storytelling.

Story Problems in Physics

Build a Laser Tripwire

Courtesy of fatllama@Flickr

I gave my final in Electronics on Tuesday (Dec. 15), and it went so well,  I can’t stop thinking about it. The format was something I haven’t tried before: 1.5 hours of written test (individual) and 1 hour of group problem solving. The problem they had to solve was to construct a laser tripwire alarm.

There are seven students in the class, so putting them all in one big group is feasible, but I was worried about students not participating or being pushed out of the project by other students. It turns out that I had nothing to worry about, they delegated and divided perfectly, coming back together to get over some hurdles and then breaking apart again to complete their roles. They passed with 12 minutes to spare, and even left it set up as a demo at their project showcase party. My only hope is that future classes work together as well as this group did.

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Physics Education Resources

It has been a while since my last list post, and I feel like focusing more on my mission for this blog. With this in mind, I would like to share a list of my favorite resources for physics teaching and physics education research (PER). Hopefully some of these are familiar, and if you use others, let me know in the comments section.

  • MIT Open Courseware
    • A growing collection of course materials from MIT. I find these to be most useful as a reference to see what other students are seeing in Physics. There can be a lot of flexibility in a curriculum and as a young professor, I like to see what other people are doing in their courses. There are a lot of reasons that I can’t use these courses verbatim, but it’s nice to see what is happening at a leading institution.
  • Concept Tests (PER@C)
    • One of the easiest things you can do for your course in Physics is to check student conceptual understanding. It is most insightful to pre- and post-test and it’s important not to use these as for-credit exams. This is a test of your abilities as a teacher more than a test of your students… the sooner you come to terms with this idea the better.
  • NCSU Concept Test links
    • Another list of concept tests for a wide variety of courses.
  • PhET Java-based Concept Simulations
    • Ever thought there had to be a better way to teach a new concept? Sometimes all it takes is a good simulation and giving students a chance to tinker around with some different scenarios. Many of the PhET sims are designed to help students build intuition as a preparation to a more thorough understanding.
  • PER Central
    • A general resource for Physics Education Research.

I’m sure there are many other good sites, but these are the ones I end up referring to quite a bit. In the future, I will discuss these topics in other posts, so feel free to contact me with any questions about how I’ve used these resources.

Teaching with Arduino


I’ve decided to use the Arduino in my electronics class this fall. The Arduino is an “open-source electronics prototyping platform based on flexible, easy-to-use hardware and software.” Even from the description it sounds like just what an electronics course needs. I finally had some time to tinker with it today, and after a few minutes I had it’s LED blinking away, and then after another few minutes it was an oscilloscope. A few minutes later it was playing a pulse-width-modulated (PWM) melody. Not bad for an hour’s work.

With a little inspiration, and my new-found confidence, I took to my first project in hopes of having a little demo to show the intro students to recruit them for my class in the fall. An hour and a half later (including fielding questions about homework and our exam tomorrow) I had a photo-resistor theramin up and running. Continue reading