Day 38 – Concrete vs Abstract



Physics 11 – Students have a really hard time interpreting graphs like the one just above this text. Once they get good at the mechanics (procedure) of the interpretation, it can be done easily and quickly. My co-worker thinks students struggle because they don’t have a procedure or set of steps to do this type of task. I agree. We could give them a procedure, but what would be the point?

Today I quizzed my students on this learning objective again (graphing constant acceleration motion), using questions like the first photo above. This gives the students a concrete idea of what the motion is. It’s easier, and while I would hope that all my students can do the 2nd graphing task, I believe that it’s the first one that we really care about.

Day 23 – Tangent Lines

Physics 11 – There was about 15 minutes of direct instruction in today’s lab. I wanted students to learn about tangent lines, so I worked through a set of arguments that would communicate how a tangent line on a position-time graph is the instantaneous velocity at that point.





So some kids get this pretty quick.  A lot of students, when asked to draw tangent lines on their position-time graphs, start drawing lines between two points. I really have no explanation for this.  While I can understand a student having a fuzzy idea of what a tangent line represents, it’s difficult to say why they would read the above and draw a line that crosses their curve in two points.

Day 38 – BFL

two motions

Physics 11 – Today was another A-Ha! day for me. It became apparent to me that my physics students were utterly confused on when to draw a best fit line and when not to.  I had seen warnings of this, but today I found just how confused the kids were.

Starting with constant velocity, we used graphs to tell the story of an objects movement – moves forwards fast, slows down, stops, then moves forward again, etc.  When conducting experiments, we collect position and clock reading data, plot the data, and analyze using best fit lines on linear relationships.  To the kids, this is all lumped into the category of “graphing” and they’re not sure when to draw lines from point to point, and when to use a BFL.

I went over the topic, talking about constant motion vs story telling, but I don’t think many kids really got it.  There was a lot of head nodding, but still a lot of confusion I think.  This is also the time of year when we really need to move on.  It’s just not worth getting into an endless rut of graphing.

So the real question is, how to motivate students that don’t get it, to come in for extra help and get past any hurdles they are experiencing?

Day 30 – Graphical Solutions to Kinematics Problems


Physics 11 – Another mostly successful day. Students were able to solve a variety of kinematics problems without having seen any kinematic equations yet. I really encourage this type of work for a few reasons.  First, I think it’s important to sketch a v-t graph regardless of the calculations because the graph clarifies the object’s motion.  Second, it keeps students away from blindly applying an equation and the dreaded statement, “I get confused on which equation to use.”  However, some problems are more easily solved with using equations directly.

Day 24 – Whiteboarding Acceleration Lab



Physics 11 – Students presented their whiteboards after completing all of their lab work.  Lots of kids got the equation of a line for the v-t graphs, which was nice to see.  They also started showing appropriate thinking such as, “I know that our spool was accelerating faster because the line is steeper.”

One issue is creeping up in the work though. Students are getting confused on when to use a Best Fit Line, and when their graphs are supposed to be discontinuous. I tried to emphasize that BFL are used when the motion is uniform (a ball rolling down the ramp, a buggy driving along the floor), and the discontinuous graphs are for graphs that tell the story of objects that change the motion (starts moving forward, slows down, turns around, etc).   There was a lot of head nodding but I’m not convinced that all students really get the difference.

Day 22 – Graphing Constant Acceleration


Physics 11 – Students continued to work on their constant acceleration lab, creating the position – time graph, and then using it to get velocity information.  I think there are some problems with this lab, where the students have to be told how to use the x-t graph to get velocity.  They get the idea but it involves a bit of hand waving.