|MadSci Network: Earth Sciences|
Daniel, Thanks for the question. The answer is definitely yes, water that is not salty can be colder than 32 degrees F or 0 degrees Celsius and not freeze. One way this could happen is if there is something besides salt dissolved in the water. Many different substances will lower or depress the freezing point. Gases like the carbon dioxide in soda pop could do it, liquids like ethylene glycol (antifreeze) could do it, or solids that dissolve like sugar could do it. Another way this could happen is by super cooling. If the water is very clean and is not agitated or disturbed it can cool well below the normal freezing point without freezing. However, if the water is disturbed or if particles like dust or sand is added to the water then it rapidly freezes. Super cooled water can occur as small floating droplets in clouds and will turn to ice when disturbed by an airplane flying through the clouds. This causes dangerous icing to occur on the airplane's wings. Atmospheric pressure will have little or no noticeable affect on the freezing point of water. It takes pressures hundreds or thousands of times greater than atmospheric pressure to make a significant change in the freezing/melting point of water/ice. Regards, Everett Rubel
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