Day 10: Using Logger Pro to Linearize

As mentioned in the last post, our second experiment provided the students a chance to work with a non-linear data set.  Today, in both courses, the student finished gathering data and then worker through a second Logger Pro Tutorial.  This time it was on linearizing.  This is another one I modified from one of the tutorials that comes with Logger Pro.  I really appreciate the fact that those tutorials can be modified, tailor-made to my classes.

One of the interesting things I find students learn about working with linear graphs is the importance of a wide range of data.  For example, some of the Advanced kids working with the simple pendulum only varied the length from, say, 10 cm to say 40cm in 5 cm increments.  Their initial period as a function of length graph did look nearly linear.  With one group, we talked about a non-linear ‘thing’ looking linear because we were looking at such a small section of the non-linear part.  The ‘thing I referenced (in addition to sketching a nonlinear graph) was the earth and looking straight out.

The suggested practice(aka homework) for the Advanced classes  for tonight was to finish plotting for data sets.  The first two were pretty straight forward.  The third one was borrowed form a colleague from our Phox Valley Physics and Physical Science Share group (an absolutely incredible group of educators that might be a blog post at another time.  Follow us on Twitter  @PhoxShare).  Anyway, the premise for the problem is a series of video clips of a car traveling at a known speed between two markers, a known distance apart.  The data given is the speed in mi/hr and the number of frames it takes the car to go between the markers. In the past I Had the students actually download the movie and count the frames. The student use the 30 frames/second frame rate to determine the time in second.  I like this problem because it provides a chance to hint at using video to gather data, foreshadowing video analysis.   It also provides another chance to point out the importance of units on numbers… the slope of the linear graph is much easier to figure out if the speed is in units with seconds rather than hours. The four problem comes from the awesomeness that is Direct Measurement Videos and the work by Peter Bohacek and Matthew Vonk (and others).  If you have not looked at these yet, STOP READING THIS and go look.  I was fortunate to attend one of the DMV sessions this summer at the AAPT  meeting.  It was at this session where I learned about the Joly Photometer and using the DMV to develop the inverse square law.  I also ‘attended’ the Global Physics Department meeting two weeks ago when Peter and Matthew presented.  Besides being just plain cool, the Joly Photometer  problem will provide an introduction to the DMV’s that we will use at various times in the course.  I’m looking forward to seeing how the students performed on this one and their impressions of the DMV’s.

The General classes will work together in class on a similar set of problems tomorrow during class.  I found it interesting that my colleague (Mike Heidke) and I decided to do this in class rather than as homework this year AND this was a topic in a few of the Modeling digest posts over the last day or two.  It makes sense to do it in class… they can ask for help and it is more likely to get completed so the practice we want the students to have, they will get.