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Question: Is it possible to cool water below its freezing point without having it freeze?
Answer: Most students learn that water freezes when its temperature falls below 32 degrees Fahrenheit or 0 degrees Celsius. If you watch the video at this Internet address (http://bit.ly/fG2qho), you will see that it is possible to cool water below its freezing point. The man in the video shakes a bottle of sub freezing water, and it magically freezes from top to bottom in a few seconds.
This phenomena is called super cooling. It happens when a liquid is cooled below its freezing point and doesn't freeze. Water and all other liquids and gases are composed of small moving particles called molecules that are much too small to see. In a liquid, the molecules are close together but not arranged in any order. As you cool any substance, the molecules slow down. When they slow down enough, the forces of attraction between neighboring molecules will cause them to stick together in a regular pattern called a crystal. The process of forming a crystal is called crystallization, or freezing. A liquid's freezing temperature depends on the strength of attraction between its molecules.
A liquid below its standard freezing point will crystalize in the presence of a seed crystal around which a regular crystal structure can form. Without a seed or nucleus, the liquid phase can be maintained below the freezing point. Shaking a super cooled liquid or scraping the side of its container will cause some molecules to form a regular crystal, and the rest of the liquid will soon follow. That is what you are seeing in the Internet video.
Drops of supercooled water often exist in clouds. Aircraft that fly through such clouds will cause the drops to freeze and stick to the wings. This will cause serious problems unless the aircraft if equipped with a de-icing system. Rain that freezes when it hits the ground is also composed of supercooled water drops.
If you want try to supercool some water, you may have more luck with distilled water from a drug store. Make sure your bottle is clean and rinse several times. Use distilled water for the final rinse. This probably won't work if you use a refrigerator freezer as the vibration from the unit's motor with likely cause your water to freeze. Try somewhere outside away from traffic on a cold night. (Warning: Leave room in the bottle for the water to expand as it freezes, and use only plastic.)
Dr. Doug Green blogs at DrDougGreen.com for educators and parents who don't have as much to read and surf as he does.
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