Why does water freeze from the top to the bottom..??
The answer lies in a very peculiar property of water. As you guessed,
the density of water of water increases as the temperature is lowered,
but below 4oC this trend is reversed. Here is a graph from The Physics Factbook.
It shows the density of liquid water vs. temperature. The reason it can
show liquid water below 0°C is that water can be supercooled, not
actually turning to ice for a long time.
So what happens is the water that is just slightly above the freezing point rises to the top so the freezing process starts there. This is the same reason why ice is at the top of a lake in the winter and not at the bottom. This is beneficial to ice skaters as well as fish and other aquatic fauna.
So what happens is the water that is just slightly above the freezing point rises to the top so the freezing process starts there. This is the same reason why ice is at the top of a lake in the winter and not at the bottom. This is beneficial to ice skaters as well as fish and other aquatic fauna.
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