Why Does Ice Float
We all know what ice basically is? It is nothing but the solid state of water. Before understanding this concept of ice floating on water we need to get aware of a term called density. Density is a physical property of an object. It is defined as the mass contained in the object per unit volume of it. In a layman’s term it is the measure of the heaviness of an object or a body having a constant volume.
Now let us try and answer the question as to why an object would float at all? An object or a body having a definite mass and occupying a space and volume would float on a similar object if it is less dense than the other i.e. the lighter the body the more floatable it is. Now consider a piece of rock. It is a substance which is more than denser than water or in other words it is heavier than water thus it sinks when thrown in water. This is exactly why the titanic sunk in water. The ship with a hole in it was heavier than the density of water.
The heaviness of a substance is a function of its molecular arrangement and the packaging of the same. More the dense more tightly packed are the molecules of the substance. For an object or a body to float it has to displace the weight of fluid equal to its own thus when ice floats on water it displaces the part of water which is equal to its own weight which is at the same time not so heavy so as to sink down the water. Hence ice floats on water. At the same time ice would never float on alcohol. We all have seen ice cubes on the glass on beer every Saturday! But this would contradict the explanation put forward above. However this is not at all contradictory and very much authenticated fact of science. This happens because the density of ice here is greater than that of the glass of alcohol.
Hence while displacing a weight equal to its own it fails to float and sinks down the glass. The maximum density of water is reached at 4 degrees and as it cools further to 0 degrees it forms ice which is less dense than the maximum density of water at 4 degree.
Conclusion : Ice floats because liquid water is 1% dense than ice. This is one of the reasons why the water in lakes and rivers freezes from top to bottom allowing water animals to thrive below and preserving aquatic life.