Logical Flow for the Collapsing Can Demo

First off, some of the ideas that this demonstration illustrates are hard to understand because there isn't any visible evidence to see - namely we can't see the gas increase in volume with just the can as the example in the demo.  So I would add a parallel demo to be done at the same time, but this would use a filled and tied balloon.

The activity would go as follows:

Fill a balloon about half way (best guess on this would work), have a student calculate its volume by treating it as a sphere, and observe the starting temperature. Write these values on the board. Have a student determine the same values for an open pop can, and write those on the board.  Volume determination for the pop can could be done by filling the can with water, then pouring the water into a graduated cylinder.  Remind them that the can is open and it is a rigid container.

Have students write down a prediction about what they think will happen if the balloon and the can are heated up, and why they think the prediction will happen. 

Heat up the two objects, ask them to describe what is happening. Discuss what is happening in the can - remember its open and a rigid container, so what would happen to the stuff inside it?  Have a student quickly measure the circumference of the balloon, and give it to you on a small piece of paper.  Record the temperatures of the two objects on the board.

After the student measures the circumference of the balloon, quickly put it into a bucket of ice water.  Have students describe what they are seeing.  Do the same for the can. Why does the can do the same thing as the balloon?  Write down the final temp of the objects on the board.

Have students talk with their partners to come up with a description of the relationship that they are seeing in this demonstration.  While they are discussing things, collect data for the circumference of the cooled balloon.

After the class agrees on one that is a fair description of what Charles' Law is introduce them to the nuts and bolts of what the law is, and have them use the data collected during this demo to figure out what the volume of the heated and cooled balloon was, the volume of the gas that started in the can after it was heated.  How can this knowledge help us understand why the can was crushed?  Since we would have talked about the particle nature of matter in class, I would ask them to explain who the number of particles of gas in the can at the beginning of the demo compared to the number of particles at the end of the heating process.  This way they would understand that there is less "stuff" inside the can, even though it has the same volume - hopefully this would help with the idea that the can collapsed, reducing volume.

After they calculate these values I would have the students compare the values they calculated to the ones that I calculated from the observational data.  Why are the values different?  What does this mean for Charles' Law?


Here is how, the logic flow would work with this further modification:

1. The balloon and the can have a specific volume at the beginning of the demonstration.
2. The size of the balloon increases as it is heated up.  The gas that was in the pop can escaped since it was open.
3. Therefore, as temperature increases, volume increases.
4. The size of balloon decreases as it is cooled.  The can gets crushed as it is cooled.
5. Therefore, as temperature decreases, volume decreases.
6. Therefore, there is a relationship between temperature and volume, that can be modeled by the equation for Charles' Law.
7. The calculated values using the equation from Charles' Law are slightly different from the values obtained from experimentation.
8. A law is an idealized relationship that is used to model the relationships that we see in nature.
9. Therefore, the data that we gathered in this real-world demo, will result in values that will be a little different from the values predicted by the law.