April 13, 2014

Modeling the Water Cycle

Last week we did one of my all time favorite demos - a model of the water cycle.

Studying the water cycle is tricky to do with inquiry because it's a global system, so it's hard to examine and manipulate. You have to scale it down, instead. There seem to be a lot of people who use a plastic baggie in a window to model the water cycle, but I've found that the bag just gets too damp inside and it's hard to see what's going on.

I found this model somewhere on the internet about 6 years ago and have been using it ever since -

The coolest part is how you can actually see condensation happening, as the water vapor turns back into a liquid, forming droplets on the bottom of the cold pan. Interestingly, at least half of my students believe that these droplets come from the ice in the pan - that the water is actually seeping through the pan. That's why the second and third questions below are so important.

The key is to have small groups (4-6 students) visit and analyze the model at least twice each. At each visit, I crouch down with the students and ask for their observations. Then I follow-up with questions:
* What is happening here?
* Where do you think those water drops came from?
* How is that possible?
* What is the ice for?
* What is happening to the water's state of matter?

I usually introduce the term "water vapor" during these small group discussions, as well.

After visiting the model, the students draw a picture in their notebook and label what they can such as Owen's labels of ice, heat, liquid, and water vapor below.
During our whole-class debrief, we add water cycle terms to each part of the drawing:
Owen's diagram
Finally, we work together to figure out how this model represents the Earth. What does the pan of ice represent? The water droplets under the pan? The heat source?

I add a few extra terms as we go and then we have a new diagram:
Owen's second diagram

This demo really makes the water cycle visible and sticks with the students throughout their thinking about it in later activities.

What's your favorite water cycle investigation?
~ Amanda

No comments:

Post a Comment