# Day 26: An uphill battle, the Buggy Bash and WB’ing the Thin Lens

After discussing the results of the Effectiveness survey the students completed yesterday, we briefly talked about graphical solutions vs. kinematic solutions.  I know this is going to be an uphill battle… helping my students see the sheer power of solving problems graphically.  The overwhelming majority prefer the equation…. just plug and chug… grrr…..   When we get to the constant acceleration problems, we’ll have another go at the graphical vs. kinematic debate. I’m pretty sure with those problems they may see the light.

We also gathered data for the Buggy Bash.   I give each group a buggy, ~20 mins to graphically determine the velocity before I pair them up.  It kills me to see the majority grab watches and tape measures.  I get it, that’s what we did with the buggies last time.  But since then, we have used the motion detectors and video analysis.  Only one or two groups in each class used one of these two approaches.  Believe it or not, I had some graph positions and time by hand on unlined paper and find the slope using the data pints they gathered… killing me I tell you!  It’ll be a rich discussion tomorrow after we’re all done.  I like the intersection crash.  They buggies have to be in motion for at least 7 seconds.  This is just far enough that the two buggy releasers can not see each other because of my lab benches.  Plus it makes it so they can’t just put them don right near each other.

General Physics:

We did a quick in class practice on a ray diagram… predict image characteristics first, then draw the ray diagram to check it. After that we WB’ed the thin lens data.  Some pretty good data:

Look closely, sloped nearly (-1.0) and intercepts almost exactly the inverse of the focal length.  Tomorrow we’ll practice it and develop how to calculate images heights.