July 30, 2013

First lab of the year - crawling before walking before running

There was a day last semester in the algebra based physics class (mechanics and thermo) towards the end of the semester when one of my students through up his hands and complained: "How am I supposed to know how to make a graph in Excel when you never taught us how?!"

On the one hand, my thoughts were that they had been writing and turning in lab reports all semester which were supposed to have had graphs on them, plus this being a college class I figured that either they would 1.) know how make a graph or 2.) ask me for help without getting frustrated.

On the other hand, my thought was the student had a point: I had not done anything with making graphs.  

Another shortcoming that many of the students I see have is never having used the equation editor in Word (or even having heard of TeX).

This Fall, I'm going to go back to one of my old favorite first labs and make it a learn to graph / introduction to equation editor / introduction to linear fits and the practice of writing a lab report exercise. 

The lab is a "Measurement of Pi" lab where students are given a bunch of circular objects and asked to experimentally determine pi. The past few times I've run this lab, I've used it more to introduce the idea that students should be able to design their own experimental techniques in lab to meet whatever goal I choose (or ideally, whatever goals the students choose.)  While I think this is an important lesson for intro physics (for engineers or not), I think I can de-emphasize the design part a bit if we use the lab to introduce some important techniques to be used throughout the lab.

So, here's my vision:
  1. Get students into groups. Each group gets a single circle but all circles will be of different size.
  2. Ask students to think of what quantities they could measure with the circles.  Have them whiteboard these ideas, then share with the rest of class.
  3. If no group comes up with value of pi for answer, ask if there is a quantity which is fundamental to all the circles, regardless of size.
  4. Ask groups to come up with a way of measuring pi. Have them whiteboard it and share with rest of class. 
  5. Have a discussion of the difference between experimental uncertainty and error as well as taking an average vs. creating a graph with linear fit.
  6. Each student makes a graph of the class data. We include error bars and a linear fit.
One of the advantages that I have at our college is using a "studio physics" approach where I have a minimum of 2-hour class meetings. (MWF are 2 hours each, TTh classes are 3 hours each: both a blessing and a curse.) Since I have long meeting times, I can piggyback lessons on top of each other. Plus, I get to walk around and help groups or individuals as needed.  Depending on how quickly we get through this activity, I would like students to start working on their lab report, too. Within the lab report, they should include the equation of best fit for the data by using the equation editor.

So there's a lot for students to digest here: graphs, best fit, uncertainty, equation editor, lab report writing.

How much class time can we devote to this?  I'm not going to spend more than a 2-hour block on this, especially since I want to do a lab where the students are more in charge of the design of the experimental procedure and analysis. (More on that idea soon!)

My fear is that we as a class will not manage the time appropriately on the first day.  I want to do FCI on the first day as well as breezing through the syllabus.  Then, if I hit them with this lab, well, it might be a lot.  On the other hand….the concept at it's core is really simple: we're going to make a graph of circumference vs diameter. So, maybe it won't be too bad.  As a backup, I will have the followup labs ready to go in case the class finishes really early.

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