FBD’s and Completing the Parallelogram

My lesson for doing a POGIL to learn about Free Body Diagrams and Completing the Parallelogram failed due to broken force probes and too few materials in general.  For the groups who had two working probes it started out well and I believe this could be a fantastic lesson if the materials were all there. 


The goal was to use spring scale force probes to measure the tension the held up a known mass.  With one force probe the weight can be inferred, then two force probes can show that the tension in each probe was reduced to about half.  From here, wedges of paper at different angles were passed out and the students would hold their probes in that orientation, measure the force, and then use the wedge on their paper to match the angle.  For all configurations, students use a scale (1 cm = 1 N) to carefully draw out scaled FBDs.  Students are guided to draw the assumed vertical force and connect dotted lines from the measured, angled forces to the top of the assumed vertical force (completing the parallelogram).


I would love to work on transforming this lesson into a 5 practices lesson to really use student responses to guide the model that we develop.  I think in the future this would be great as two lessons.  The first one to practice using the devices, measuring out the vectors and learning about how mass and weight are related by using different objects and making a graph.  The second would be this lesson where they look at forces from different angles. 


This lesson came from a long “head scratching” experience of how to help students discover free body diagrams, rather than just explaining the steps.  I really want to help students discover more and guide the work that we do and I’m very happy to read the 5 Practices to help with that.  I always thought Free Body Diagrams was a pretty dry topic to learn at first (though incredibly useful) and it took forever for me to come up with a lesson that puts the focus on the students doing science instead of just taking lecture notes.  I think a lot of discovery lessons via the 5 Practices, followed by Hewitt’s Conceptual Physics Worksheets can create a strong conceptual base that is student driven.  Future tasks are to develop strong student discovery based lessons to learn Motion Maps, Energy LOL Diagrams (Bar charts), and Momentum Bar Charts.



I’m just finishing week two of a three week project on building bridges.  The goal of the project is to further study forces and begin working on engineering practices.  One of my pedagogy-based goals is to connect individual lessons to a general goal and help students create a narrative about what they are learning.  I’ve been interested in the idea of students building a story of physics as a way to understand each topic and hopefully see a clear picture of why they are learning the content.  I don’t know if projects are necessary to achieve this, but so far it is helping me connect the pieces with them and constantly refer back to a singular goal of building a bridge that don’t break under a specified weight, using as little material as possible.

In order to be successful with this project, I gave students a schedule of work to be completed each day (both in class and at home) and a rubric for all graded parts of the project.  This has helped my students keep on track and have clear instructions for any work that is completed at home.  It also keeps me on track because I had to make sure every lesson ended with the students being capable of completing the required work.  I’ve done this kind of backwards design before, but I’ve never done it while planning three weeks of class.  I like the organization that this gives me and I think it gives a much clearer picture to the students.

I also have a narrative with fill in the blanks that goes with this project.  It is several short paragraphs and we complete a new paragraph after each class.  This idea is borrowed from my mentor teacher back when I was student teaching.  We also made a WDIL (What Did I Learn) in this same format and students would call out the blanks as I read the paragraph before they left.  I find this really helps put the entire class period into perspective and it gives a summary of what they learned.  Several students have told me that they really like this.

So far, I really like the organization that this project has brought to my classroom.  I don’t know if I can always come up with a good project for everything, but I hope to do more projects in the future.