Day 6

3:09 P.M.

Block 2,4,5 (Physics 1,2)

Screen Shot 2013-08-28 at 3.10.24 PM

This idea came to me as through the years as I tried giving students very specific instruction on how to do labs which invariably failed to get them a) motivated b) clear on what they should do c) to the learning objective.

Today We did modeling lab called the spaghetti bridge lab . The link by the way is NOT my own, and I did not use a document like this in class. It is worth clicking on the link if you are reading this post to get an idea of what the lab is about.

In short a strand of uncooked spaghetti is suspended over a gap at its ends.  A cup hangs below it and marbles are placed into the cup until the strand breaks. Students record the number of marbles it takes to break the strand and the depression of the strand in whatever length unit they want. This is done for a single strand, 2,3,4 and ideally 5 strands of spaghetti.

What I like about the modeling approach is that the opener is typically something like “What are some questions we can ask about this system?” , or “What can we measure about this system?”

I notice that modeling instruction leans towards the second question. I tend to avoid opening that way because I imagine myself as a jaded high school senior thinking “Why would I want to measure anything about this system?”

The question “What questions can we ask?” are great because I can open with a demonstration of the suspended stand. I can drop a marble in, a second marble in, a third etc. I can then say something like “Should I go on?”

If the students say, “Yes!” I can let them know that that is what they will be doing. Then I can address the fact that in a physics class. We try to quantify everything and “number of marbles it takes to break a strand…” or other similar phrasing is only half the story.

As a facilitator I can then ask something like, “Well, how do we measure if its about to break?”

Nearly all the students say something like, “See how much it bends”

THAT’S the breakthrough idea that leads us to finding the easiest way to measure the bending. Inevitable this leads them to the dependent variable of measuring the vertical distance the cup moves as more marbles are added.

Why I don’t like suggesting a lab technique

I don’t like suggesting lab measurement techniques to my students because they always come up with better lab set ups than I do. I am being completely serious. My background is in theoretical chemical physics. I solve things on paper and write programs. I am one of the worst spatial thinkers I know, and arranging laboratory equipment in an experiment like this is certainly spatial thinking.

In my next post, I want to share out some of the great ideas my students had in doing this lab, and some of the suggestions they had for improving it and making it more rigorous.

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