"ice floats on water because water______ when it freezes, which causes it to be less _________than water".
602290
is ligher              dense
549327
Freezing water expands.
858193
Yes.  Salt water freezes at a lower tempurature than fresh water. \n\nThat is why we use salt to melt ice on sidewalks in the winter.
279658
Ice floats on water because it is less dense than water, meaning it has fewer molecules per volume. This is because of the Hydrogen bonds. In fact, while other substances contract when solidified, water expands. That's why it's less dense, and not because it has air inside. Furthermore, when the temperature decreases and reaches 4 degrees Celsius, every water molecule is Hydrogen-bonded to 4 other molecules near it. Then, they form into a crystal lattice structure, and it holds them further apart.
4010
Fist of all let me correct that, the word Ice has no singular; on the contrary you might as well lower the external temps or purify the ice.
246690
Water actually freezes on the top, around from the edges, first. Water also expands when frozen. As the water freezes inwards, towards the centre, a little hole is created in under the right conditions the expansion can create a frozen spike on the ice cube.
807422
When water freezes, it expands because the molecules form into a crystal lattice. The expansion causes ice to be less dense than liquid water and as a result, it floats.
284203
Ice lowers the melting point of water, so it causes the ice to turn to liquid water and break up.  If it's *really* cold, this doesn't help.
628194
It decreases ever so slightly.\n\nFrozen water has a larger volume than liquid water (this can be inferred from the fact that it is less dense; alternatively you can show it is less dense if you know it has a bigger volume), so as more water goes from solid (ice) -> liquid (water), the total volume decreases.\n\npeople have been saying it increases; this is incorrect! When you put water in a cup and leave it in the freezer, the cup breaks. This is because water EXPANDS as it turns into ice; therefore it will CONTRACT when it melts.
155920
Uh, the ice melts.\n\nWhen all the ice melts, you'll find that the water level of your beverage has gone down a little.  This is because water expands when frozen, which is the opposite of pretty much everything else.
507086
Because water is most dense at 39 deg. F, therefore ice is lighter than water.
858544
Because water expands when it freezes..\nTherefore ice is of larger volume than the water it originated from\ntherefore it is less dense..
745528
Interesting theory, however water expands when it freezes.  It has no problem melting under pressure.
873711
Not quite right.  It is most dense at 4 degrees C.  If it didn't, the water would freeze from the bottom up.  As it approaches 0 degrees, it becomes less dense and rises above the more dense warmer water and freezes on the surface and goes down.  Otherwise, fish would be on top of the ice and die after it froze.
278046
Depends on what the "mass" is (its density)!  If the mass is more dense than water, then the mass is heavier - if the mass is less dense than water, then the mass is lighter than water.  Ice is the solid form of water and it is less dense, therefore it floats.
426143
Ice floats on water because it is less dense than water.\n\nAs water cools past 5 degrees celsius, the density of the water actually decreases.  Since ice is water molecules at <0 degrees celsius, it is less dense than liquid water ( greater than 0 degrees), so it floats.\n\nfrom a molecular point of view, the H2O molecules in ice is equally spaced apart, whereas H20 in liquid state are able to slide past each other (i.e. closer to each other), so it is more dense than ice.
706444
Density= Mass/Volume.  When water freezes, its volume increases. This is why a frozen bottle of water expands to the point of bursting. By the formula, if volume increases and Mass stays the same, then the value of density decreases.  Thus, this is why ice floats and is less dense than water.  When the ice melts, the reverse happens in that its volume decreases and again by the formula, density will increase.   Tahdaaaa!!