Re: Why does ice float in water?

Kate,
You are both wrong.

Ice floats because the weight of the water that the ice displaces is greater 
than the weight of the ice itself. This is the principle of buoyancy. The 
difference in the two weights is the buoyant force acting on the ice.

The same volume of water can have two different weights, if one is liquid and 
the other is solid [ice] because the density [weight per unit volume] of liquid 
water is greater than the density of ice. Water is one of the very few 
materials that exhibit this behavior.
 
Earth is fortunate that water ice does expand and float. Just imagine what 
would happen if ice sank instead! All the water in the world would freeze and 
sink to the bottom of the oceans; the next bit of water would freeze and sink, 
too. In no time at all, earth would be nothing more than a spherical ice ball 
floating in space. [The late Isaac Asimov explored this far more eloquently 
that I just did in one of his many short science articles...]

There are also about 9 different 'ices', called iceI, iceII, iceIII etc that 
are beyond the scope of your question.

Ken