Like most physics teachers that model, I start the constant velocity unit with the (cv) dune buggy lab. And, again like most, I have my own little changes that I have made to suit my own purposes. Here they are:
1. Through discussion, we develop the concept of position (not distance travelled) measured with a number line and clock reading, measured with a stop watch as the two variables. I allow the advanced students to decide which variable to set as the independent variable. This means when WB’ing, we get an interesting variety of graphs.
2. Once the students are out in hallway setting up, I talk individually with each group to answer any questions and to ‘guide them’ by assigning an initial position (not to be confused with the origin) and a direction of travel. Half of the groups are assigned the negative direction and are told to imagine they have the negative side of the number line on the tape measure they are using; they just need to imagine little (-) signs on the tape measure. They also need to add the (-) to their data. To make it even more interesting, I have some start at a(+) position and head in the negative direction or vice versa. These groups also usually pass through the origin. Doing this also provides some nice variation when we WB, and, in the end shows a number of different possibilities.
SIDEBAR: Assigning the direction and initial position, especially the negative ones, usually allows me to see which students are still stuck on distance travelled because they always get a positive slope and no intercept, when the should have a negative and some intercept.
3. I alter the dune buggies when I put the cells in. I have 3 or 4 of the older ones still working. I can put cells in with the polarity reversed so the buggies run ‘backwards’ or ‘in reverse’. If I am really on top of things, I’ll make sure a group that is supposed to go in the positive direction gets one so we can talk about using forward and backward to describe direction. I also add aluminum slugs to some so they are really slow.
I’m looking forward to the WB’ing on Monday.
These classes were able to see and talk about the graphing assessment they took. We also completed the Mass on a Spring version of the We Got The Beat Challenge. Here are two student samples that were really pretty good:
Did you notice the Wilberforce Pendulum action on that one?
Monday, this group will start in on Geometric Optics. More on that later.