Circles and Data

September 3, 2010

So, as part of this whole Inquiry thing, I’ll be asking my students to do some data analysis. Nothing that ought to be too challenging, but some manipulations they may have never been asked to do. In the spirit of “education” and all that, I thought it might be prudent to actually teach them the methods I expect them to use. Revolutionary, right? I know…I think I might be on to something here 🙂

[As an aside, last week I had a student walk out of a different class because he “[doesn’t] like to have [his] time wasted” with the “tedious bullshit” of having to learn the software he’ll be using to take data for the rest of the semester. Students. Sheesh.]

We started with something I assumed everyone was already familiar with: circles. In groups of 4-6 the students measured the diameter and circumference of 7 circles. I showed them how to find the averages and manipulate data in Excel, and as a class we made a chart of Circumference vs. Radius. Unsurprisingly, we had a nice straight line! I explained how this means we have a proportional relationship between our variables, and we can begin to write the equation: C ∝ r. Now this is a good start, but we’d like to do better….insert a trendline, find the slope, no big surprises: it’s π! We can now write a real equation: C = πr. Ta Da!!!!

So that’s all well and good, but not all of our relationships are going to be linear… what do we do when our initial graph isn’t a straight line? Try squaring things. For our forced example, Area would be the next logical step. Unfortunately, we were running out of time to have the class measure the areas of the circles, so I fudged some data. I showed them a graph of A vs. r (hey! that line’s curvy!!!) and A vs. r2 (hey! that line’s straight!!!! Now we know that A ∝ r2!). Again with the trendline, and Ta Da!!!! A = π r2

So how’d it all turn out? I think it went OK. I have some figuring-out to do with the data-sharing problem. Google Docs doesn’t have a trendline function (not an easy one, anyway), and I can’t seem to set the correct permissions on our college’s shared Student drive to allow them to save changes to an Excel file. Irritating. I didn’t leave enough time to complete all the activities, and they were definitely antsy by the end. I had to remind them that class is not over until 8:50, so would they please sit back down at 8:45 and listen for the next five minutes? It was a reasonable introduction to Excel, I think, but overall it was less the student-directed activity I wanted it to be, and after the introductory measuring it felt primarily like a lecture in which they were following along on their own laptops instead of taking notes. If I do this again next year, I would allot at least two hours for the activity, and give them a cheat-sheet of Excel commands so that they could work more on their own, and I could circle through the class to help as needed.

But no one, as far as I could tell, left the room muttering “tedious bullshit” under their breath. That’s a win, right?


Last night (Thursday) was our first set of labs: 6-7:40PM and 8-9:40PM. That second one gets a bit late.

I’ve been doing this lab for a couple of semesters now. I’ve always thought it was a good introduction to the Scientific Method, and a nice way to fit in a lab when they haven’t really learned enough content do do much of anything else.

So just what is the Great Hot Coco Mystery? Well, make yourself a cup of instant hot cocoa: hot water in a ceramic mug, packet of cocoa poured in on top, metal spoon to stir. Stir it up a bit, then stop. Begin tapping your spoon on the bottom of the mug and listen carefully…as you continue to tap, the pitch of the tapping will rise. Stir a bit more, and when you resume tapping the pitch will have dropped (though not as low as at the start), and then proceed with rising some more. This process can be continued for quite some time, and the rise in pitch becomes quite obvious.

So what is the “experiment” part of the experiment? The students (who have brought their own mugs and spoons. Yay! No washing for me!) are given a largish number of cocoa packets (8/group of 4 seems to be enough), and access to a number of other products: Sugar Free Cocoa; Fat Free Cocoa; Cocoa with Marshmallows; instant coffee crystals; instant apple cider; lemonade; instant cappuccino mix; water heating on hot-plates; hot and cold tap water; ice. They must design at least three investigations, with at least three variations within that investigation (still working on some of the terminology here…bear with me). For example, say they want to investigate whether the effect (rising pitch) is related to water temperature. They could then make a cup of cocoa with boiling water, hot tap water, and cold tap water. They could add icy water for a fourth variation. They are allowed to collaborate with other groups to pool or share resources; though I don’t think anyone did last night.

With 20 minutes left in class, we share the “results”. I stand at the board and ask each group to tell me one of their investigations, and its results. Then the other groups are asked whether they can confirm or contradict these findings. We talk about experimental procedure…are you really changing just one variable at a time, or did you (intentionally or unknowingly) change multiple initial conditions? Why is that maybe not the best idea?
Given what the class has found, can we make any definitive statements as to what the *cause* of the effect might be?

In the last 5 or so minutes, I ask what would they want to do next…given more resources, more tools, more time, how would they set up the next investigation. Some want thermometers, or a way to measure the temperature change of the mug. Many want microphones to record the pitch change. Something that dissolves in cold water, in addition to the lemonade.

I like this as an intro lab for a number of reasons. It’s accessible…nearly everyone has made themselves a cup of hot cocoa. If not cocoa specifically, then something similar. But few people have ever tapped their spoon on the bottom. The effect is not too subtle…it doesn’t take motion detectors or infrared thermometers to detect (not that there’s anything wrong with those things. However, I have a strongish belief that computer-assisted labs are over-used in introductory physics classes). And it’s weird! I mean, who doesn’t want to know *why* this happens? But it’s also still mysterious. I don’t know the answer. The source from which I developed the lab didn’t know the answer. The students are not going to determine the answer in one night during lab. And that’s OK! That’s how Science is done! You don’t get The Answer at the end of a two hour period…hopefully you just get a bit of the way there.

End Note: I modified this experiment from a presentation I’d found on the internet. Someone (AAPT???) doing a demonstration for other instructors. I can’t find it with a quick google search, but I have the original material at school. I’ll update with references when I’m back on Tuesday.

And so it begins…

August 26, 2010

First lecture last Tuesday night. I explained the philosophy behind the course, how we would be implementing that, and the manner in which it would be graded. So far, no one has revolted (which is a step up from last semester). While it is physics, and very few of my students are super excited to be there, they seemed relatively engaged throughout. Which is saying alot for a 3 hour lecture that ends at 9pm…

So what is it I’m doing? First off, a bit about my class. I teach Physics Concepts at a community college. Most of the students who come through my class are not going to be physicicts or engineers (though there are a small percentage in that group). There are a few PSEO (high school) students, but the bulk of enrollees are attempting to get into the Radiation Technology program, or perhaps Prosthetics and Orthotics. There is also the occasional pre-Education major. The course is used by the other degree programs primarily as a “weed out” course — they *need* at least a B in the class to get into Rad Tech, but competition is high so an A is much better. Students will use very little of the content they learn in my course in their later studies. So what is the point of my class? What do I want my students to take away? I’ve decided (and my department agrees with me) that our main goal should be to strengthen Critical Thinking skills, in the context of Physics.

Back in April I was invited (along with the rest of the Science department) to a workhop at Winona State University on Inquiry Methods in the classroom. About a week before, I’d been directed to Shawn Cornally’s blog Think Thank Thunk … if you’ve happened to read it, you know that Mr. Cornally is highly supportive of Inquiry methods *and* SBG. At the WSU conference they told us the story of why they’d begun implementing Inquiry labs…it turns out that many of their students, even those who planned on a STEM major, were lacking in Critical Thinking skills (as measured by the Lawson CTSR). What they’ve found at Winona State is that if low-scoring students are first placed in a “Prep-Chem” or “Prep-Physics” class which focuses on building Critical Thinking skills, these students overwhelmingly go on to be successful in their general physics/chem courses (the calculus-based ones).

Now, I imagine that “Inquiry” is one of those terms that has multiple uses and meanings. The Think Thank Thunk method is genius, however I can’t yet see how I could make it work with my class schedule…and lack of power tools. The definition given at the Winona workshop (and the one I’m following) can be boiled down to this: Data first, Theory later. Traditionally, students do experiments that (hopefully) confirm the equation that was learned the other day in lecture. This semester, we will do experiments to collect data, and somewhat collectively interpret that data to hopefully arrive at the appropriate theory. Or near it, at least. If we can identify relationships between variables, I will be relatively happy. More details on all this later….

Standards…in formulating my standards I went with Jason Buell’s method, from over at Always Formative.

…more on the Standards later. For now, it is 10am, and I need to feed my children some breakfast. And then go to work…I’ve got lab tonight, after all.

If any experienced bloggers should happen to read this, please know I am new to blogging. I’m still working on some of the etiquette, especially regarding links, trackbacks, and pingbacks and all. If there’s something I should be doing, please let me know!

…overcome the first obstacle of starting a blog: the name.   You know, something relevant, but not too pretentious and obscure (Shoulders of Giants, Everything Else is just Stamp Collecting), or silly and inside-joke-from-long-ago-y (What a Bunch of Bosons, Mmmmmmm….slanty).    Thus, “uNclear Physics” which, yes, is a not-so-clever play on Nuclear Physics, my topic of study in graduate school. It is also how most of my students view their coursework.   And now, it’s the title of my brand new baby blog.  About Physics.  And the teaching of Physics.  And specifically, a documentation of my journey through simultaneously implementing Standards Based Grading (SBG) and Inquiry Methods in my Physics Concepts course.

This is my blog.  I hope you like it.