Sunday, March 06, 2016

The Bells of Pasco

One of the first things I purchased for my physics program (using other people's money) was Pasco's Lenz's Law Demonstrator. At the time (1988), it was $55. I remember thinking that was a tidy sum, and that I should probably have cobbled together a home-made version of it myself. As my mentor, Steve Keith, often said, "Why buy something for $50 when you can make it yourself for $60?" But there I was, with the "store-bought" version and a bit of guilt.

The apparatus worked great for its intended purpose, but I felt it was important to milk this thing for all its pedagogical potential. I supplemented it with an otherwise identical length of PVC tube to show tubes made of insulating materials produced no effect, and I used an otherwise identical length of EMT to show that iron produced "too much" effect. (Who doesn't love a Goldilocks situation?)

Eventually, I found the aluminum tube did a great job as a blow gun: I was able to shatter whiteboard marker pens that I blew through the tube and toward solid doors or walls, accelerating the pens to speeds unlawful on local highways. The description of this application became my first published article in The Physics Teacher. The inimitable Don Rathjen of the Exploratorium Teacher Institute designed a simpler, safer version of this demo that he called The Marshmallow Puff Tube.

I also found that the tube was capable of producing lovely tones when struck gently at an end with a croquet mallet. The trick there was knowing where to hold the tube (with as light a grip as possible). Serendipitous experimentation shows that different tones can be produced, depending on where along the tube you hold it. The point is amplified if you hold the tube very near the end: acoustically, it's as dead as the proverbial doornail.

The other day I was returning our set of aluminum Pasco Introductory Dynamics System tracks to their storage space when I decided to give them a bonk with the old mallet. I was able to get a nice set of tones out of them. Not as pure and simple as with the Lenz's law tube, but not bad. The Pasco Basic Optics bench, though similar in its extruded aluminum simplicity, was a disappointment as a bell. I blame the permanently attached rubber feet for putting a damper on things.

What exactly one might do with the knowledge that a Pasco track is capable of producing nice tones, I do not know. If you think of something, please share it in the comments. If Bree or I think of something, we'll share it here, too.

And what about that $55 capital outlay in 1988? Considering it's been seen by over 150 students per year for three demos each year for at least 25 years, the expense amortizes out to $55/(150 × 3 × 25) = $0.0049 (less than half a cent) for each student per use in class. There are some things in education that cost more but are worth less. Whatever burden of guilt I attached to the demo purchase has long since been replaced by a buoyant spirit of instructional utility.

No comments: