Science Bell Ringer for Grades 6–8: Why ice floats
A free science bell ringer for grades 6–8. Put the prompt on the board as students walk in, give them three to five minutes, then go over it together. The answer and teacher notes are in the box below the prompt.
The prompt
Most substances get denser when they freeze, so the solid sinks in its own liquid. Water is different: ice floats. Explain why, and predict about how much of an ice cube sits above the water line.
Answer and teacher notes
When water freezes, its molecules line up in a regular pattern (a lattice) that holds them farther apart than in liquid water. That makes ice about 9 percent less dense than liquid water, and anything less dense than water floats. Because ice's density is about 90 percent of water's, roughly 10 percent of an ice cube or iceberg sits above the surface.
Extension: why does it matter for fish that lakes freeze from the top down instead of the bottom up?
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