Day 26: Working with CA Graphs


Physics 11 Today was spent working through graphs of objects moving with constant acceleration.  The majority of students got it ok, but almost everyone needed a few corrections or challenges.  A few students were starting to hit the wall on clearly understanding how these graphical descriptions fit together.

The students that had problems reminded me a lot of what I saw when teaching Math 10 last year.  They would show understanding but then a few minutes later would get stuck. And I mean really stuck.  I think this is a perfect example of cognitive overload.  Cognitive Load Theory (CLT) informs us that when a person’s cognition is taxed to its limit, the brain is no longer able to transfer knowledge from short term memory to long term memory (that’s my lay person’s explanation). I believe this is what I see with a few students in physics.

I believe that the best way to deal with these situations is to first try and recognize that it’s happening.  If a kid is getting stuck, telling them to go home and do more practice probably won’t help a ton. In the particular situation of CA graphs, I offered three strategies for students to use to help them work through confusion.

Strategy 1

I encouraged them to break each part of the position-time graph into separate sections.  For each section, they then write in words what the object is doing.  All the kids can do this (moves forward, moves backwards, moves faster, etc).  For each section, I then have them explain how the motion affects velocity (constant, getting faster, getting slower, etc).  Now they graph what they wrote down for velocity

The above may seem formulaic, and it is.  However, it is a series of steps that doesn’t dance around conceptual understanding.  It’s a way for students to verbalize their guide to the motion.

Strategy 2

The next strategy I suggested was to take the position-time graph and sketch tangents on it.  As long as the student understands the correlation between slope of the tangent line and velocity, they can build the velocity-time graph. Again, the strategy still depends on a conceptual understanding and is not just a series of steps.

Strategy 3

The third strategy I proposed was… oh who am I kidding. I can’t remember what the third strategy was.  It seemed like a good idea at the time. If I remember it later I’ll update this post.


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