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Investigation: Back and Forth, or Not

Melt It

Check Your Understanding: Choosing the Variable

Freeze It Back

Check Your Understanding: The Freezing Asymmetry

Fizz! The One-Way Change

Check Your Understanding: Reversible vs. One-Way

What Melts Fastest?

Check Your Understanding: Two Different Questions

Lessons 4–7: children melt and freeze on purpose, trigger a fizzing reaction that can never be undone, and rank solids by how easily they melt — building the evidence for the unit's reversible/not-reversible question.

The investigation phase: children melt and freeze water back and forth, trigger a fizzing reaction with no way back, and rank solids by how easily they melt.

Changes You Can and Can't Undo

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