The Positive Physics Difference
Breaking down traditional problems into manageable skill-sets.
Example: Unit 2: Forces, Packet 2: Introduction to Force Calculations
The End Goal: Solve Rigorous Problems
We push our students to be able to solve rigorous, traditional problems as shown below.
However, while we begin with the end in mind, our students do not begin with these “complete problems,” as is the case in a
traditional physics course. For example, in order to solve problems in the Forces Unit, students must correctly apply four skills:
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Have a conceptual understanding of the problem
Apply various mathematical operations.
Draw a force diagram (free-body diagram)
Analyze the force diagram
When students only get one “at bat” with each skill while working on this lengthy problem, they do not get enough repetitions with
each skill, and often end up not being able to correctly complete the problem.
In the Positive Physics approach, we break the complete problems down into well-defined skill sets, and give students a series of
problems that isolate one skill. Our rule of thumb is that every problem in the series should focus solely on the selected skill and
take less than thirty seconds to complete. Only after mastering each skill do we ask students to put the skills together and solve the
complete problem.
The problems shown above would appear in the second packet of our Forces Unit. The steps we use to isolate the individual skills
for these problems are shown below.
Skill A: Conceptual Understanding
First, we ensure that all students know all necessary definitions and can articulate all necessary concepts.
Skill B: Mathematical Tools
Next, we ensure that we equip students with all necessary mathematical tools. In this packet, students need to be able to solve
equations, perform unit conversions and round numbers correctly. In subsequent packets, students would also practice
trigonometry as part of this skill.
Note that our students show their work by listing each quantity and using our reference sheet rather than writing equations. Our
approach is designed to focus on the physics and ensure that we can reach all students, regardless of their math foundation.
However, the problems that we present in the Positive Physics will work for other teachers who choose to use the algebraic
approach.
Skill C: Force Diagrams
Using the conceptual understanding of the principles, students are then asked to draw correct force diagrams, showing all the forces
that act on the object. The ability to draw the correct diagram is critical to solving the problem, but is often overlooked. We actually
dedicate one full packet and one class period in each subsequent packet in the Forces Unit to practicing drawing force diagrams.
During this time the students do not perform any calculations so that they can practice this skill many times in a short period of time.
An additional benefit of drawing force diagrams without the accompanying calculations is we can add more complex situations to
ensure a complete understanding of the principle.
Skill D: Force Diagram Analysis
After drawing the free-body diagram, students need to be able to analyze the free-body diagram to find the net force, or work
backwards, using the net force to find an unknown force. We realized that this point of the problem is where students most often
get confused when using a traditional approach. It was in response to this situation where our breakthrough occurred and the
Positive Physics approach was created. This step always occurs in the middle of a traditional problem and can only result in success
if the force diagram was correctly drawn. We realized that if we gave students questions with the correct force diagram already
drawn we could isolate the analysis step of the problem and give students questions that just focused on this skill and again allow
many repetitions in a short period of time.
Solving Complete Problems
After mastering the four skills listed above, the student is prepared to to solve the rigorous, complete problems, like those shown at
the top. We have found that after students have a conceptual understanding of the problem, can apply the necessary mathematical
operations and can draw and analyze force diagrams they are very successful combining the skills to solve rigorous, complete
problems, and many times are able to complete the problems before we even do an example as a class. And, perhaps most
importantly, they are no longer intimidated by complete problems and approach physics with the belief that they are capable of
success and begin to understand how much of their world is explained by physics.