Permeability Part 2 - Which is the best sponge?
New York’s Urban Ecosystem Lessons
This is the second in a series of four lessons on the permeability of surfaces in a watershed. These lessons can be done together or individually. If you plan on doing all the lessons in the permeability series, then you should consider doing them in the order suggested: Part 1, 2, 3, and then 4. This series works particularly well after the Watersheds series of lessons. In this lesson, students will design, perform, report to each other, and provide feedback on their own original experiments to compare different types of sponges. Students will also consider the distinction between absorbancey and permeability. If you follow the Permeability lesson series, then your students will use these same sponges in a later lesson, Part 4, to create a model of the permeability of surfaces in a local watershed you chose to focus on. This provides motivation for needing to know how the different sponges interact with water.
Materials and Resources
- Aluminum trays
- Aluminum foil (or something else non-absorbent like plastic, fleece or wool) different types of sponges -- details in Tips for Teachers water bottle
- A way of sharing students’ data, which will depend on your timing and classroom setup. This could be writing on a board, using a projector, photocopying for the next day, etc.
Before you get started
Tips for Teachers
Decide ahead of time what area you want students to model, and prepare the satellite images and possibly the outdoor expedition accordingly. It’s important that students share some familiarity with this location, whether it’s the location of your Oyster Restoration Station, the neighborhood of the school, or some other place that is accessible and part of your students’ daily lives. Since you’ll be visiting the ORS with your class anyway, that could be an excellent choice. Notes on scheduling lessons in which students design their own experiments Because some groups will work faster than others, it’s important to be flexible in two ways: You need to let groups work until a critical mass have completed their testing. This amount of time will vary, and in some ways, the longer they take, the better, if that means they are really thinking and talking about what they are doing! That means you need to be prepared to let the activity run over several days, if groups are remaining focused and able to dig deeply at this moment. You also need to be prepared to wrap up quickly if groups are losing focus or not able to dig deeply at this moment. No matter how flexible you are, not every group will get all the way through their testing before you want to move on for the good of the class as a whole. That’s ok! It’s important to help the students feel that that’s ok by making it clear that, as long as they are focused on their work and thinking carefully about what they’re working on, the process is more important than the result. A very important way of accomplishing this subtle goal is to listen in on groups for several minutes at a time, so you know something about their processes, and, when the opportunities present themselves, praise students for their engaged, thoughtful processes. Don’t wait for the final product to offer well-earned praise! Sponge Suggestions use a car-washing sponge to represent loose, very permeable soil use a dishwashing sponge to represent compacted, less-permeable soil use a green scouring sponge to represent compacted, barely-permeable soil use something that does not absorb like aluminum foil, plastic, or even certain types of fleece or wool where the water beads up and runs off, to represent an impermeable surface use a hard sponge that has totally dried up for the “bone-dry sponge”, to represent dry soil
Perform this ‘demonstration’:
Where everyone can see, spill some water. You might enjoy making it look like an accident. Then point out your different materials, and ask students and let them raucously call out which sponge they think you should use to clean it up. Appear undecided for a few moments, to give everyone a chance to shout out their ideas. Perhaps toss a few sponges to students who aren’t involved yet, or who say all sponges are the same. Then choose something that won’t work very well, and try it. Let students shout at you to make a better choice. Wonder aloud, “why isn’t this working?” Let students call out their theories while you try another. Keep trying materials until you’re satisfied with the students’ energy and with the clean-up of the spill.
- Shift gears now, praising your students if they’ve done a good job generating ideas, questions, and/or productive disagreements.
Tell your students that ultimately, they will create a model of the permeability of surfaces in the watershed location you have chosen. In order to do that, they need to know: what are the surfaces around that location, and how absorbent are the materials we have available for our model? You’ll spend some time on both, and this lesson is for learning what we need to know about our model materials. That is the purpose of doing these sponge experiments.
Separate students into small groups.
Hand out Observation/Inference Chart.
Each group gets an aluminum tray, a measuring cup and several types of sponges.
Ask each group to observe the different sponges and describe what they look like in the “Observation” section of the Observation/Inference Chart.
Based on these observations, predict a ranking showing which sponges will hold the most and least water, and record predictions in the “Inferences/Predictions” section of the Observation/Inference Chart.
Ask each group to design an experiment to test the absorbency of the different sponges. For this you can use the
Handout: Which is the best sponge?
Each group shows you their experimental design, i.e. the filled-in Handout: which is the best sponge? You can ask them questions about their plan, and ask them to solve problems with the plan before you approve it, as you see fit.
- After you’ve approved students’ experimental designs, suggest that they create a data table in which they will record their actual results, and then let them run their experiments.
Compile groups’ results so everyone can see all of them. You might also decide to select a subset of each group’s results to share at first. Depending on your classroom setup, you might need to do this outside of class time, and continue the lesson the next day.
Lead a discussion in which you ask students to compare their predictions with their results.
Ask them questions like:
Which sponge/material held the most water? Why do you think this was the case?
Which sponge/material held the least? Why do you think this was the case?
If groups’ results vary (and they probably will!), how can we make sense of that? (This can get you into a discussion where students want to know how other groups conducted their experiments. Quite possibly they can provide both positive feedback and constructive criticism on one another’s experimental design!)
How did the size of the holes in the sponge relate to how much water it could hold? Are there other factors that seemed to help you predict the absorbency of each sponge? Are there factors that seemed to mislead you in your predictions?
- Which sponge would you use for which job in daily life? Why?
Now remind your students that in addition to finding out which is the best sponge, they are also going to use sponges in their models of the location you have chosen, to represent surfaces with different permeability. Ask them first to write individually about, and then to discuss:
Is absorbency the same thing as permeability? Put another way, do you want the same things in a sponge that you want in a nice permeable surface in your watershed?
How are the two properties, absorbency and permeability, similar, and how are they different?
Referring back to the Handout: Surface Types, which sponges and other materials do they think would best represent which surface types based on permeability?
It’s possible that this could lead students to want to retest all their materials, now focusing on permeability instead of absorbency. That’s wonderful! If you can possibly swing it, we encourage you to postpone the other activities and go for it!
You can use the same kinds of handouts and formats, but the content will be new, richer, and deeper, because:
students will have asked to do this
They will have the opportunity to refine their experimental designs
- They can engage in ongoing discussion with one another about each other’s experiments and analyses