We finished up talking about microstates and entropy which finished the ideal gas model. The class applauded. Then I asked the question, "how could we add gravity to our ideal gas model." Groans.

So many models build on the next. I'm telling a story. I'm trying to show logical connections between one idea and the next. And what a better way to extend the ideal gas model than to add gravity? How does the pressure relate to the depth of the fluid? And, since we can't really see differences in pressure that well with gases, why not look to liquids? Hence the lab.

We got very similar results, with slopes of 9200 pascals per meter. One group decided the slope would be negative, since we kept going deeper (and lower) to measure higher pressures. We figured out what the 9200 pascals per meter meant, and why it was smaller than theory would predict. We had a few minutes at the end of class to practice this new mathematical relationship.