Why does ice float?
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See it another way
Why does ice float in water? - George Zaidan and Charles Morton
Watch water molecules settle into an open hexagonal pattern that leaves ice roomier than liquid water.
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What else makes you wonder?
Would ice from salty ocean water float the same way?
Salt sneaks in between the water bits and changes how tightly they pack — so the weigh-off might not come out quite the same.
Do other liquids spread out and get lighter when they freeze too?
Most don't — they pack tighter and their solid version sinks in the puddle. Water is the rebel. What could make it break the rule?
How much of a giant iceberg hides underwater where ships can't see?
If only a tenth pokes above, where is all the rest — and how huge would the hidden part of a mountain-sized berg be?
More to explore
After you watchWhy does ice float?
The short answer
Ice floats in liquid water because it has lower density: the water molecules occupy more space in the open ice structure. Freezing a fixed sample without losing water changes its volume, not its mass.
Try this next
- How would the result change if both containers were instead filled to the same final line? Make a prediction and explain what you would keep the same in a fair comparison.
The whole story
How it works
Equal volumes of ice and water contain different masses. But equal starting masses remain equal when one freezes without loss. In the model, both balance pans still hold 240 grams while the ice takes more room.
What people get wrong
Lower density does not mean a particular sample loses mass when it freezes. Comparing equal final volumes and comparing equal starting amounts are different experiments.
The catch
Ice floating at a pond surface helps insulate the water below. Expansion on freezing can also damage confined pipes or containers. The illustration uses roomy containers so no water is lost.
Questions kids ask
Why does ice float?
Ice floats in liquid water because it has lower density: the water molecules occupy more space in the open ice structure. Freezing a fixed sample without losing water changes its volume, not its mass.
What does the experiment compare?
Start with equal 240-gram water samples. Freeze one without losing water and leave room for expansion. Predict the balance result, then release it to compare the conserved masses.
What is this model leaving out?
Ice floating at a pond surface helps insulate the water below. Expansion on freezing can also damage confined pipes or containers. The illustration uses roomy containers so no water is lost.
Talk about it
- Two samples start with 240 grams of water each. Freeze one without losing water: does the balance tilt or stay level?
- What changed in the pictures that supports your idea?
- How would the result change if both containers were instead filled to the same final line?
For grown-ups
Ordinary ice Ih near 0 °C has density about 0.917 g/cm³, below liquid water. Hydrogen bonding supports an open structure. Mass is conserved for a closed sample; volume increases. Buoyancy depends on the displaced fluid relative to the object, not on a rule that all lighter objects float.