A Re-Done Demo: The Collapsing Can

What happens if you heat up an opened pop can, then put it up-side-down in a container of cool water? Well if you watch this video you can see what happens.  This demonstration shows the relationship between temperature and volume.  In the end, the ideas behind why the can gets crushed, really don't get conveyed to the observer.

In the clip from the Spangler Science TV, this demonstration has more of a "let me show you what is going on" tone rather than an exploratory tone.  In my experience, those demos that had that exploratory tone were the ones that kept me interested, actually made me think, and I learned the most from.  When I would modify this demonstration, I would go through tell students what the set up was, then do the demo and ask: "What is happening?"  My goal with showing what happens then asking students to describe what they are seeing is to have students figure out a way to explain in their own words.  The way that I scaffold the conversation will help students get to the final conclusion about the temperature and pressure relationship. I would ask questions that would get students to explain that when the can was heated up, the air inside increased in volume and some air was pushed out of the can.  Then I would start asking questions about what would happen to the air inside the can when the it was cooled down with the water.  After a little more discussion, a few more times crushing the can, we as a class would get to the conclusion that volume varies with temperature.  Only after students got this far, would I tell them about the formalized equation and wording that goes along with Charles Law, that way they would have an understanding of the law without getting confused by how wonderfully worded Charles Law is.

The discussions that I would encourage can be done in several ways: large group, small group, think-pair-share, etc.  Depending on what level of my students and the point we were at in the progression of the discussion, I would choose an activity that would benefit the students.  For instance if I were to see that there were more puzzled looks than looks of understanding, I would have students do a think-pair-share, that way I would tap the "more knowledgeable peers" in the class to help get some ideas across in a way that other students may be able to understand more easily.

I like the idea of showing the demonstration as a precursor to discussion, and having students describe what they are seeing - much like what a scientist would do.  Scientists go would do something then try to explain what they are seeing, based on their prior knowledge and the evidence that they have.  Students would also have to be creative in how they were coming up with the conclusions from the data they were interpreting.  I would be able to tie in the NOS by asking questions that get the students to look at the process that got them to the ideas that we were getting at.