Does the water level rises when an ice cube is melted?
Question
A cube of ice floats in water at 0°C. Heat is supplied just enough to melt the ice without changing the temperature. Will the water level rise, fall, or stay the same?
Short Answer
The water level stays the same.
Why It Stays The Same
For a floating object, Archimedes’ principle says the object displaces a volume of water whose weight equals the object’s weight.
Before melting:
- the floating ice displaces water equal to the ice’s weight.
After melting:
- that same mass of ice becomes liquid water,
- and occupies exactly the amount of water volume that matches its own weight.
So the displaced volume before melting matches the added liquid volume after melting.
Another way to say it: floating ice has already “reserved” the correct volume in the glass through displacement. When it melts, it simply fills that reserved volume as liquid water.
Exam Trap To Avoid
Students often focus on “ice is less dense than water” and conclude the level must rise when density changes. Density matters for floating height, but the decisive argument here is equal weight displacement.
Extension
If you place a dense object (for example, a metal ball) on top of the floating ice, the final level can change after melting because the displacement story is different.
This is a common extension in tests: always identify what is floating, what is sinking, and which fluid provides buoyant force. Those details decide whether level change is zero, positive, or negative.
Internal Links
Lesson Links
- Internal Energy, Thermal Energy & Temperature
- Latent Heat & Specific Latent Heat
- Energy Transfer Via Convection