Why does ice float on water?

Ice floats on water because it is less dense than water.

is as mass per unit volume of a substance. By saying that ice is less dense than water, we mean that a sample of ice will take up more space than a sample of water that has the same mass.

Ice and water are both made of the same element ##H_2O##, otherwise known as Hydrogen Dioxide. At sufficiently cold temperatures, usually around 0 degrees Celsius (32 degrees Fahrenheit), water undergoes a to ice called freezing. This is because as the temperature becomes colder, the water molecules lose energy and move less.

The that form when water freezes into ice allow the molecules to be spaced farther apart, thus making them take more space, decreasing the overall density and making it float in the water.

The reason that density determines if something will float or sink is because, as stated by Newton's third law:

##F = ma## where ##F## is force, ##m## is mass and ##a## is acceleration.

and so the gravitational force for two substances with the same volume will be greater for the substance with higher mass and thus higher density.