Thursday, October 8, 2015

Will It Float?

In Science Methods this week we have been learning more about what inquiry-infused science learning looks like. I really like the "5 E's" learning cycle for managing an inquiry-infused science class, and I've been recommending this to my students. (This model was developed by Rodger Bybee and colleagues in the Biological Sciences Curriculum Study; you can read their executive summary if you want more details...)

The 5 E's are a way of organizing learning activities for a student-centered, constructivist approach to science learning. The 5 E's are five "movements" in an inquiry learning cycle that describe what the teacher and students are doing. In a nutshell:

Engage - The teacher provides some sort of hook (a discrepant event, a connection to students' world, etc.) to foster curiosity and set the stage. This provides motivation and a need-to-know to set up the inquiry.

Explore - The students conduct a first-hand investigation to develop their thinking about the science concept to be learned. This movement often exposes students misconceptions about science concepts, and also gives them concrete experiences that can provide the basis of new learning.

Explain - In this movement, both the students and the teacher have the opportunity to do some explaining. The students explain their current thinking, based on their experiences in the Explore movement. The teacher has the opportunity to probe their thinking, ask questions, help them voice their ideas...and provide direct instruction to help students think more scientifically about the concepts being considered. This is the movement where teachers help mediate students' understanding of the content.

Elaborate - The students then have the opportunity to continue working with these new ideas, extending their thinking through another learning activity. This might be another hands-on investigation, further research, or some sort of creative response that incorporates the science concepts. They key is that students continue to develop their thinking about the science content, elaborating on what they have previously learned in the Explore and Explain movements.

Evaluate - Finally, students and teacher work together to find out what the students are now thinking about the concepts. Assessment of learning happens here, with the students (hopefully) able to say, "I used to think...but now I think..."

We had previously learned about the 5 E's learning cycle, but I wanted my students to experience a learning cycle firsthand. So, we took a couple class meetings to learn about floating and sinking, a common elementary science topic. Here's what we did:


I began by showing students a collection of pieces of wood and a collection of rocks. I set these on a table near a small aquarium full of water. I asked them what would happen if we dropped a piece of wood into the aquarium. (My college students looked at me a little funny.) One of them suggested it would float. So...we tried it, and, lo-and-behold, it did float.

I then asked what would happen if I dropped a rock into the water. A student suggested--with a smile--that it would sink. And of course, when we dropped it in the water, it a rock.

We kept dropping wood and rocks into the water, and all the wood floated, and all the rocks sank...until the last pair. The last block of wood a rock...and the last rock...floated on top of the water as if it were made of styrofoam.

The students were hooked. Many had seen pumice before (a type of rock that floats in water) but none had seen sinking wood. We had a short conversation about the wood and rocks, and then I asked a "magic question": So...if wood usually floats...and rocks usually sink, but not always...what makes things float and sink?

This question was the driving question for the inquiring that followed.


To explore this question, I gave my students a classic challenge: build a "barge" that can keep at least 10 large steel washers afloat. I gave each group a square of aluminum foil (about 30 cm x 30 cm--that's about 1 foot square), six extra long drinking straws, and a 30 cm piece of masking tape to get started.

Students dove in to the challenge. They began folding foil, bending straws, taping things together, and trying out their barges. Many had barges that could keep a few washers above sea level, but many were struggling. The tubs of water I had provided for the testing were too narrow for the extra long straws. Finally one student asked, "Do you have some scissors I can borrow? These straws are too long!" (I love it when they ask!) I handed her a pair of scissors, of course. And immediately other students began asking questions:

"Do we need to use the tape?"

"Do we need to use the straws?"

"Our barge looks like a canoe and it keeps tipping over...what if we start over? Can we have another piece of foil to try this again?"

Soon, most every group had a barge that could keep at least 10 washers afloat. Most had many more than that. The strongest barge had close to 50 washers onboard before it went under!

It was time for a little clean up (and mopping up) before we talked about what we found out.


I asked the students this question: "What did we find out about floating and sinking?" They had some great responses:

  • "Washers sink."
  • "Aluminum was more buoyant than we expected."
  • "Straws filled with water will still float."
  • "Having 'sides' on your barge helps keep the water out."
  • "Displacement is key--you can't put all the weight in one spot."
From this list of things they found out, I asked a few more probing questions about some of the terms they used: "buoyant" and "displacement." Eventually, we settled on some working definitions for these terms. 
  • We decided to use "floatability" for buoyant--the idea that the force of the water pushing up was greater than the force of gravity pulling down.
  • We decided to use "spread-out-ness" for displacement--the idea that you had to distribute the weight by spreading it out across the surface of the water.
From here, I was able to give some prodding to help them understand that the weight wasn't really the issue for whether or not something would float. We could lay a piece of foil on the surface of the water and it would float just like that. If I plopped a stack of 10 washers down in the center, it would sink immediately. But if I spread those 10 washers out across the surface, it easily continued to float without any other modifications to the "barge"--no other materials, and no "sides" required.

(For the purposes of this learning cycle, I did not get into density, per se, but that would have been the next place we could go as a way of explaining floating and sinking.)


From here, I gave students another challenge:

We have learned that some things float. Let's call them "floaters." We have also learned that some things sink. Let's call them "sinkers." What if something neither "floats" up at the surface nor "sinks" all the way to the bottom? Let's call these "flinkers" (because they sort of float, and sort of sink...)
Work as a team to try and build a flinker!

I had a pile of all kinds of junk on hand for them to work at building a flinker: old jars, plastic tubs, and bottles, nails, pennies, modeling clay, straws, paper clips, styrofoam cups, washers, masking tape, baggies, plastic cups, bits of balsa wood...the whole junk drawer dumped out for them to rifle through.

Teams got right to work, and began building, testing, rebuilding, re-testing, tweaking, and testing some more.

It was harder than they thought!

After a fair bit of time to have a go at it, several groups were getting close. Here was the nearest attempt:

That is a simple plastic cup, filled with water, pushed down into the tub, held steady, and then the hand slowly withdrawn. It did bob up and down a bit, but in the minute or so we watched, it neither touched the bottom nor broke the surface. (Way to go, team!)

Again, some clean-up, with quite a lot of discussion and sharing along the way.


As we came back together as a whole group, I asked them to try and explain what would have to be true about a "flinker" in terms of buoyancy ("floatability") and displacement ("spread-out-ness.") They began talking with their table partners to try and explain this. Most groups settled on the idea that the force of buoyancy pushing up and the force of gravity pulling down would have to be balanced, and to do this meant that the mass of the "flinker" had to be spread out a bit, but not "too much." (This last part was harder for them to articulate, honestly.)

Finally, I turned their attention back to the floating rock (pumice) and sinking wood (ironwood) that I had showed them at the beginning.

"Can you explain now what is going on with this weird rock that makes it float? Can you explain what is going on with this weird wood that makes it sink?"

Partner talk again; most every group was able to articulate it in terms of the "spread-out-ness" of the weight and the "floatability" of the material: the rock is not very "floatable," but if you spread it out enough, it will float. Likewise, the wood is usually very "floatable," but if you gather its mass close together, it will sink.

(Hey, you know what? That's basically the concept of density...which is what makes things float or sink!)


So this was our learning cycle. At the end of the 5 E's, I asked the students to evaluate their experience: what did they notice about their positioning as students? (Active learners!) About my positioning as teacher? (An arranger of the learning environment, and a questioner first off.) About how they encountered the content? (Through exploration and investigation, developing ideas, and understanding by doing.)

I considered the lesson a success!

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