# Day 15: WB the Buggy Lab and Why we start the General class with Optics

It was a different style of WB’ing for the students.  Today each group presented its ‘ buggy experiment. I like to have each group present and explain the procedure followed because I find it can help set the tone for the class… we use discussion ALOT, and one has to be perfectly clear when explaining things.  As I explained in the previous post, I guide each group in terms of an initial position and direction.  To help with connecting a group’s procedure to everyone else’s, and to the graph, I make a suggestion about how to organize some of it:

As expected, there was a mixture of graphs… some position as a function of time (clock reading), and some time as a function of position.  In all the classes, the students were able to identify the meaning of the vertical intercept for all the graphs AND for some of the graphs, the meaning of the horizontal intercept.  Most classes also hinted at the sign on the slope indicating direction of travel.  Tomorrow will build the conceptual meaning of each slope THEN give it a name… thank you very much Arons!

General Physics:

As explained previously, we start the General classes with Geometric Optics.  This was an idea I picked up from Jeff Elmer (formerly of Oshkosh North).  The advantages are just too numerous to ignore.  Here they are as I see them:

1.  Super high interest—> a bunch of really cool things to see, literally.

2.  It can be taught in a very conceptual manner.  Using ray diagrams, linguistic representations and essentially two ‘equations’  (the thin lens equation and what we call the similar triangles equation relating the heights and image and object distances) all of lenses and mirrors can be handled.  This puts the math-phobic students at ease as we start.  It gets them used to being a physics student without worrying about all the equations they may have heard about.

3.  The General kids get ‘behind’ the Advanced kids.  We start the Advanced class with Kinematics.  They are done with the constant velocity and constant acceleration models by the time the general gets there.  This means that when the ‘generals’ ask their ‘advanced’ friends for help with kinematics, most of the advanced kids understand it well enough to help in the way we want them to using our terminology…

So, what did we do today?  On the spur of the moment, we dusted off an old activity that we had gotten away from… the pinhole camera.  We will use it to build the ray model for light that we will use as the main ‘pictorial representation’ for our optics. It reinforces that we imagine the light to travel in a particular direction in a straight line. We can represent this with an arrow or ray.  It also naturally lends itself to drawing the ray diagrams to explain some of the observations we see with the pinhole camera.