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Cold water boils faster than hot water

FALSE

Updated: 2008/06/09 PM 5:04:32   Comment

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It is physically impossible for cold water to boil faster

This is myth that falls into the "suspend the laws of physics" category.  The October 21, 1998 issue of Scientific American states: "Cold water does not boil faster than hot water. The rate of heating of a liquid depends on the magnitude of the temperature difference between the liquid and its surroundings (the flame on the stove, for instance). As a result, cold water will be absorbing heat faster while it is still cold; once it gets up to the temperature of hot water, the heating rate slows down and from there it takes just as long to bring it to a boil as the water that was hot to begin with. Because it takes cold water some time to reach the temperature of hot water, cold water clearly takes longer to boil than hot water does. There may be some psychological effect at play; cold water starts boiling sooner than one might expect because of the aforementioned greater heat absorption rate when water is colder."[1]

But cold water does heat faster than warm water!

"Apparently this myth has its origins in the fact that cold water heats faster than warm water. A pot of water at 40o will reach 60o faster than a pot of 70o water will reach 90o, given the same heat source. This is because the rate of heat transfer is proportional to the temperature differential between the heat source and the item being heated. But the cooler water will always take longer to boil.[3]

And hot water can sometimes freeze faster than cold water

It is true, however, that warm water sometimes freezes faster than cold water. This happens only under very specialized conditions, and has nothing to do with boiling water."[3]

Sources:

  1. Scientific American

  2. New York Times
  3. Kitchen Myths

*Note, however, that many people generally avoid using hot tap water for cooking on the theory that the hot water is not as clean from sitting in the water heater or from leaching substances from the pipes (a worry in houses with old plumbing).



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