Name: Jason G.
Why does milk freeze from the bottom up? Ponds freeze
from top down.
I do not think your premise is correct. The specific gravity of milk is
about 1.030-1.032 making it somewhat denser than water. So if ice forms when
milk begins to freeze, it would float. Now, if the freezing continues and
de-stabilizes the dispersion of cream and milk solids, these may float to
the top, but that is a whole different process.
Ponds, and other bodies of water, are VERY SPECIAL when it comes to
freezing. Almost all liquids freeze from the bottom up. This is because,
usually, atoms get more tightly packed when they freeze. The empty space
between the atoms cuts down. It is kind of like compressing a hollow ball
into a solid object. A hollow aluminum ball will float, while that same
aluminum squeezed into a solid lump of foil will sink. Water is special
when it freezes. If you look at snowflakes with a magnifying glass, you
will see many empty spaces. Ice has more empty space in it than water. As
a result, frozen water floats on liquid water. This property keeps ice on
top of the water so the sun can melt it in the spring. If water froze like
other liquids, all the ice would sink to the bottom, never to melt again.
In a few years, the oceans would be frozen solid.
Dr. Ken Mellendorf
Illinois Central College
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Update: June 2012