A cube of ice floats in a glass of water, the entire system at 0°C. Just enough heat is supplied to melt the ice cube without altering the system’s temperature. Does the water level rise, fall or stay the same?
The water level stays the same. An ice cube floats only because its water has expanded during crystallization. Its weight remains the same as the weight of the water that formed it. Since a floating body displaces its own weight, the melted ice cube will provide the same amount of water as the volume of water it displaced when frozen.