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Name: Jason G.
Status: student
Age: 13
Location: N/A
Country: N/A
Date: 2001-2002


Question:
Why does milk freeze from the bottom up? Ponds freeze from top down.


Replies:
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.

Vince Calder


Jason,

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
Physics Instructor
Illinois Central College



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