Why does ice float on water?

    It is a matter of common experience that ice floats on water. Howsoever large the size of ice may be, it will not sink. Even icebergs keep on floating in the sea. Do you know why ice floats on water?

    The law of floatation of bodies was given by the Greek scienctist Archimedes. According to this law, whenever a body is placed in water, it is acted upon by two forces-the weight of the body acting downwards and the buoyant force of water acting upwards. If the weight of the body is equal to or less than the upthrust of water, the body floats on water. In other words, if the weight of the body is equal to or less than the weight of the water displaced by it, it will float on water. On the other hand, if the weight of the body is more than the weight of water displaced, the body will sink in water. Hence a body floats when its weight is equal to the weight of water displaced by it. Since the weight of wood is half of the weight of equal volume of water, that is why half of wood is under water, while the other half is above water. Similarly, the weight of cork is one-fifth of the weight of the water displaced by it, so one-fifth of cork is under water while the rest is above water. You can understand the floatation of ice also, on the basis of this law.
    In general, when a liquid changes to solid, it contracts because its molecules come closer to each other in the solid state. As a result of this, the volume of the substance decreases or its density increases. Hence a substance becomes heavier in solid state, than in the liquid state.