- #36
Mark M
- 527
- 1
The Usenet FAQ has a very good entry about the Mpemba effect:
http://math.ucr.edu/home/baez/physics/General/hot_water.html
http://math.ucr.edu/home/baez/physics/General/hot_water.html
krd said:No, but he's trying to repeat an effect that has already been observed.
The whole Mpemba combination - and I think they have prizes for a whole bunch of similar problems. It's not just that should be able to repeat it, but you also need a theory to make it repeatable.
From the article:Mark M said:The Usenet FAQ has a very good entry about the Mpemba effect:
http://math.ucr.edu/home/baez/physics/General/hot_water.html
My problem with this is that there is an implied repeat-ability problem here and if the experiment is highly dependent on initial conditions, but isn't repeatable, then you can't with confidence say that it is real and not, for example, a product of experimental error. See: Cold Fusion.Hot water can in fact freeze faster than cold water for a wide range of experimental conditions. This phenomenon is extremely counterintuitive, and surprising even to most scientists, but it is in fact real...
It is still not known exactly why this happens...
Why hasn't modern science answered this seemingly simple question about cooling water? The main problem is that the time it takes water to freeze is highly sensitive to a number of details in the experimental setup, such as the shape and size of the container, the shape and size of the refrigeration unit, the gas and impurity content of the water, how the time of freezing is defined, and so on. Because of this sensitivity, while experiments have generally agreed that the Mpemba effect occurs, they disagree over the conditions under which it occurs, and thus about why it occurs.
krd said:You know when you get wet, you feel cold?...That's because the thin layer of warm air is no longer over your skin. So, your body cools quicker. But that principle is not a factor in the Mpemba effect.
Studiot said:Well feyn, that certainly answers my comment in post 16,
If the two test vessels have a different temperature distribution they can have the same average temperature and still coll at different rate. It may be debatable whether the liquid can be represented by one temperture if it is not uniform but that would seem a good way forward.