Freezing Water Bottle – Reflections

Why is this science?

There are several features of what the students are doing that make it a clear example of science.

First, the students are working to reconcile an inconsistency between the model they’ve been working with and their observations of the world. They consider different options for reconciling the inconsistency: (1) some students tweak the existing model in ways that more closely align with their observations (Jack A and Ben), and (2) other students conjecture that the expansion they observe when water freezes may be a special case when the water is in close proximity to air (Inger’s idea).

Second, students cite evidence and propose experiments to support their conjectures. For example, DC says, “You guys know when you put your cup full of water, and then you put ice cubes in it and they crack- the ice crack? That’s the- that’s the um air pockets opening,” to support the idea that air might be getting trapped between the water molecules. Megan proposes a hypothetical scenario to determine whether the presence of air is responsible for the expansion: “If like you had a water bottle with like somehow you had no air in it if it would still like [expand].”

Finally, Jack B, in particular, continuously pushes Ben and Jack to explain why water expands when it freezes. He believes that a their model should provide a mechanism for the phenomenon, not just an account of it.

What contributed?

Various aspects of what was going on contributed to initiating and sustaining this episode.

The students recognizing an inconsistency between model and experience
The central question that students are grappling with emerges from an inconsistency between their model and their experience. The model predicts that hotter molecules move farther away from each other and colder molecules move closer together. However, their observation contradicts this prediction–water expands when frozen! This inconsistency proves to be genuinely problematic for students, especially Jack A and Ben, who attempt to add new features to the existing model as a way to reconcile the inconsistency. Ben develops a model in which molecules merge together and then buckle to form pockets and Jack A develops a model in which air pockets get trapped between the molecules as they join together to form ice.

Tension around and refinement of the question
From the beginning, there seemed to be disagreement over the nature of the problem. Jack A argued that packing together makes something smaller, which raised the question of how water “packing together” to make ice could be larger. DC argued for a simple solution, with the analogy that people huddled together form a larger unit. This tension drove students to focus on articulating the problem itself.

Students’ agency over the flow of the conversation
From the start, we see students taking agentive roles in leading the discussion and determining who gets the floor to speak and who their audience is: they authored ideas and initiated questions, they interacted directly with each other’s ideas, evaluated each other’s arguments, negotiated the nature of the controversy, and refocused the conversation. This agency was both taken by the students and granted by the teacher.

Availability and use of material resources
Students used various physical resources as they reasoned about the question. They used the board to draw and communicate ideas. They had sheets of paper and notebooks to use in constructing models. Ben, for instance, demonstrated his idea with two notebooks (representing molecules): he brought the notebooks close together then bended them to create an empty space in between them (representing the air pockets in ice). Jack A crumpled a piece of paper to illustrate his idea of how air gets trapped as the molecules get closer together.

The teacher made space for students’ ideas
Most of the time during this episode, Mrs. Filner, who was sitting in the back of the room, was listening to the students and allowing them to lead the discussion. They, in turn, seemed comfortable addressing each other without her facilitation. Occasionally, she directed the conversation, to focus attention on a particular student. She also joined in to articulate the essence of a debated issue, such as when the students wrestled over whether packing together makes something larger or smaller: “But if we all squished ourselves together, I don’t think we all of a sudden are bigger!”

Students’ strong feelings
In several ways, students’ feelings seemed to motivate their participation and to be part of their communicating their positions in the debate. To start, Jack A’s puzzlement drove his persistence in posing and articulating the question, and it communicated to others that there was something he was genuinely trying to understand. Students also showed irritation, Jack A over students not understanding his question and Jack B over the lack of mechanism in Ben’s explanation: “But then how does it exPAND like what you’re saying?” And they showed excitement, such as Ben in declaring, “I need two pieces of paper.”