July 31, 2013

Toothpick / matchstick lab idea

Since I am going to use the "Measure the value of pi" lab for introducing graphing, equation editors and potentially writing a lab report, I want to have a lab where the goals and the experimental procedure is developed by the students in the class from top to bottom as much as possible.  Here's my idea:

I plan to give students a taped box of matches or toothpicks with a random number of matchsticks or toothpicks in them. Alternatively, I could have a single full box that students could have with the ability to put as many or as few matchsticks or toothpicks in as they choose.  Hmmm….going to have to think about that one.

There will be only one rule: students cannot open any box until the lab is done and the report is written.

I'm going to ask students: What do you want to know about the box?  I want them to write their questions down before they say anything. Then I'll have them discuss in small groups with whiteboards.  Then we'll have a short all-class discussion of the questions they are interested in.

I am hoping that the groups will come up with at least "How many matchsticks (or toothpicks) are in my box?" But I would also be thrilled if they came up with questions like "What is the mass of a single matchstick (or toothpick)?" and "What is the mass of the box (and tape)?"  These are my goals for the lab, it will be interesting to see what the class comes up with. If needed, we can have a discussion which leads us to these goals.

I will have prepared ahead of time several identical boxes each with a unique number of matchsticks or toothpicks in them and marked on the box itself. I will try to use the same amount of tape on each box, so each box is as identical as possible.

This is the first lab where I will encourage the students determine the process by which they will meet the goals of the lab. I don't know if it's the best way to encourage this process, but it should be a good follow up to the pi lab.  I don't think there are many ways to find the mass of a single matchstick or toothpick, the mass of the box and the unknown number in the initial box, other than using a linear fit model, but I'll leave the students to figure that out.

I want to have students make predictions or guesses for the quantities they want to measure before doing the lab. I think it will be interesting to see how these guesses compare to the experimental data. We can have some discussions about orders of magnitude if there are wildly varying guesses.

Then we'll do the lab. I tried this myself and it went really quickly.  There's not much to do other than mass the boxes and record the data.

I want to make sure every student has a graph of the data and has used equation editor to express their best fit line equation.  If time permits, I want to have them start to write the lab report.

My worry with this lab is again that it is too easy.  I hope that by emphasizing the students' control of the goals and procedure it will hold their attention to the end of the lab.  Plus, if we finish early, I have an idea for the next lab to do.  :-)

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.

July 03, 2013

Back in the (scientific) python business!

The above five lines of python represent the accomplishment of a (small) summer goal of mine: to have one cohesive python install with all of my favorite python packages for writing code for physics classes and research.

I don't know what happened earlier this year, but I had b0rked up my python install on my school laptop. I have a Macbook Pro, and was running into all sorts of problems: 32 bit vs. 64 bit, which install of python to use and whether or not I could use matplotlib and vpython at the same time.

What I ended up with was two installs of python: one that could use vpython and one that could use matplotlib, but never the two at the same time.

As you can see in the screenshot, I have everything working now with the excellent enthought distribution of python. What I learned today was that ALL  the packages in the vpython dmg file are required to run vpython. I don't remember my original thought process which led me to believe I didn't need the other packages, but I did. Also, I learned today that you can't always (simply) run vpython calls from the python shell, unless you limit the rate of displaying frames by putting rate() inside a loop.  More on that later, maybe.

I know the above packages have significant overlap (scipy extends numpy, pylab has matplotlib, etc.) but I've used each of those in various forms, so I wanted to be able to call any of them without having to THINK about it.  Done.

Okay, so if you made it this far into this post, you deserve a reward. How about 8 tutorials on scientific python programming? My favorites are the SciPy tutorial and the excellent matplotlib tutorial.