nature · FOLLOW YOUR CURIOSITY
Why does solid water float?
An ice cube stays near the surface of your drink. Being solid is not what decides whether something sinks.
Explore the interactive discovery →
Start with what you see
Density compares mass with volume. Ordinary ice is less dense than liquid water: the same mass occupies more space after freezing. A floating cube displaces enough water to balance its weight before the whole cube is submerged.
What is happening?
Do not confuse lower density with lower total mass. A large block of ice can be much heavier than a glass of water and still float in a lake. The comparison that matters is mass per unit volume, not which object is bigger.
Try a concrete example
Compare equal volumes first: a container filled with ordinary ice has less mass than the same volume of liquid water. Then compare equal masses: freezing that water makes it occupy more space. These are two ways of describing the same density difference. Floating introduces another step: the cube pushes water aside until the displaced water’s weight balances its own. The part above the surface is therefore a consequence of the density difference, not evidence that the cube has no weight.
AN IDEA TO TAKE WITH YOU
Floating depends on relative density, not on whether an object is solid.
Follow a connection
How can tiny animals build a reef? →
Compare how internal structure changes the properties of two familiar solids.
Sources and transparency
USGS · Water Density
Accessed: 2026-10-31
University of Texas Marine Science Institute · Floating Ice
Accessed: 2026-10-31
Illustrations explain an idea. Sources are available above.