Trivia: Hot Water Freezes Faster Than Cold Water

1. Matt
   September 28th, 2007 at 2:35 am

   The molecules in hot water move slower than cold water just like ice. This was rediscovered? I’ve known that since elementary…

2. Vexorg
   September 28th, 2007 at 2:53 am

   According to the article, That’s “Tanzanian”, not Tasmanian.

3. greg laden
   September 28th, 2007 at 6:14 am

   It is, of coruse, simply not true that hot water freezes faster than cold water. Not counter intuitive, just wrong.

   Most of the time the explanation for the alleged observation is as simple as the fact that given two exactly identical “quantities” of hot and cold water, there is less hot water than cold water.

   In other words, it is not true that hot freezes before cold … what is true is that people sometimes make poor observations and draw incorrect conclusions.

4. Lee McKenzie
   September 28th, 2007 at 7:16 am

   The rate of cooling of an object varies and slows as that object approaches the temperature of the cooling source. The experiment should start with identical masses of water in identical containers and engineering to prevent evaporation (a plastic film will do). Because of the higher temperature differential between the hot water and the cold water, the hot water will initially cool faster than the cold water. As the hot and cold water cools to closer to the source temperature, both of their rates of cooling will slow. However, at a given point, the hot water will reach the starting temperature of the cold water. At the point it reaches the starting temperature of the cold water, it will have the same temperature differential and therefore the same rate of cooling with which the cold water started. It will also take the same amount of time for the “hot” water to freeze from the temperature at which the cold water started. Because of the length of time that expired for the hot water to cool to the starting temperature of the cold water, it will always take longer for the hot water to cool. That’s physics.

5. Nick
   September 28th, 2007 at 7:39 am

   Greg is correct. My little step sister did this as a 6th grade science project. It doesn’t freeze faster.

6. Doctor Fedora
   September 28th, 2007 at 8:00 am

   Hooray for bad science!

   For what it’s worth, water that’s been heated up AND ALLOWED TO COOL BACK DOWN to a comparable temperature will freeze faster than water of that temperature that was never heated, but that’s only because heating the water removes dissolved gases. It also provides you with far less cloudy ice.

7. saehn
   September 28th, 2007 at 8:24 am

   Read the article and the reference articles. This headline is inaccurate sensationalism, but the point is that VERY hot water (90c-195f) does freeze faster than hot water (80c-175f).

8. noah
   September 28th, 2007 at 8:46 am

   Greg laden is absolutely correct, don’t believe everything you read on Wikipedia. I love Neatorama, it gets me through most mornings, usually the posts are right on the money, not this time

9. sadtomato
   September 28th, 2007 at 9:15 am

   I think the CBC radio show Quirks and Quarks addressed this years ago and said that it’s only true outside (as opposed to in a freezer). So if you try the experiment at home with ice cube tray the hot water will not freeze faster.

10. Monster
    September 28th, 2007 at 10:24 am

    http://www.sciam.com/askexpert_question.cfm?articleID=0008EB6B-6C7E-1C 71-9EB7809EC588F2D7

11. Alex
    September 28th, 2007 at 11:56 am

    Oops, thanks vexorg - I’ve fixed the simple Tanzania/Tazmania mistake. My mind is kind of sloppy with that sort of stuff.

    But I stand by that the Mpemba effect exists, although physicists are unsure of the reason why. Here’s an article from Physics World for all you non-believers, and I quote:

    In 1995 German physicist David Auerbach at the Max Planck Institute for Fluid Dynamics in Göttingen looked at the role of supercooling in the Mpemba effect. But what he found only made things more complicated. He observed that hot water froze at a higher temperature than cold and therefore in a sense froze “first”. However, the cold water took less time to reach its supercooled state and so seemed to freeze “faster”. To add to the confusion, earlier researchers had reported the opposite: that initially hot water could be supercooled to lower temperatures than cold water. In 1948 Noah Dorsey of the US National Bureau of Standards argued that this is because heating expels impurity particles that acted as nucleation sites for ice. It has been claimed that this effect leads to hot-water pipes bursting more readily than cold, since deeper supercooling leads to ice fingers that advance right across the pipe and block the flow, while freezing nearer to 0 °C just produces a sheath of ice on the pipe surfaces with an open channel in the centre.

12. Alex
    September 28th, 2007 at 12:37 pm

    To Matt: The molecules in hot water move slower than cold water just like ice.

    Absolutely the opposite, mate!

    To greg laden: In other words, it is not true that hot freezes before cold … what is true is that people sometimes make poor observations and draw incorrect conclusions.

    This experiment had been done carefully by physicists, who discovered the existence of the phenomenon but has yet to understand its cause.

    To Doctor Fedora: For what it’s worth, water that’s been heated up AND ALLOWED TO COOL BACK DOWN to a comparable temperature will freeze faster than water of that temperature that was never heated, but that’s only because heating the water removes dissolved gases.

    From my understanding, this experiment (conducted by Logan McCarty, a chemist at Harvard University) still used hot water and cold water - not hot water that’s allowed to cool back down. His conclusion was that gases were responsible for the effect (i.e. degassed cold water freeze first).

    To saen: Read the article and the reference articles. This headline is inaccurate sensationalism, but the point is that VERY hot water (90c-195f) does freeze faster than hot water (80c-175f).

    That may be so, but there were a lot of experiments that used hot water (90° C) and cold water (18° C). See: D. Auerbach, Supercooling and the Mpemba effect; when hot water freezes quicker than cold, Am. J. Phys. 63 (1995) 882-885. Link

13. John Mc
    September 28th, 2007 at 1:34 pm

    Take to paper cups and fill them with water.
    One with hot, the other with cold.
    Put them in your freezer.
    The cold one will turn to ice first.

    We had a bet on this at work. The cold cup turned to ice first.

    phenomenon my ass!

14. Alex
    September 28th, 2007 at 2:46 pm

    It’s going to be hard to do the experiment properly in your freezer, because the rate of cooling isn’t uniform and putting a hot object in the freezer will change the cooling environment. You’d need a walk in freezer.

15. DanR
    September 30th, 2007 at 5:40 pm

    This experiment works because the hot water rapidly melts the ice on which it is sat, forming a very good liquid coupling from the ice to the vessel. This then freezes quickly into a tight join, which conducts the heat away from the hot liquid MUCH more. The water in the “hot” vessel with the coupled base loses heat maybe 1000 times faster than the “cold” vessel sitting on a nice insulating layer of fluffy snow, and can in this instance, overtake it and freeze first.

    People who run barefoot over hot coals (1200 degrees C) look ever so impressive and empowered, but I bet they can’t walk over a hotplate at a mere 70 degrees C if it has a layer of oil over it - same insulation / conduction phenomenon.

    BTW that wikipedia entry is a blatant attempt to technobamboozle laypeople. “Continuum mechanics”, “partial differential equations” and CFD’s trouble with turbulent flow has absolutely nothing to do with this; they are mathematical techniques used to describe or solve known heat transfer problems, they are not physical phenomenon that we don’t understand.

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