anand@utastro.UUCP (Anand Sivaramakrishnan) (06/03/85)
There have been quite a few experiments done on this topic. One that I recall was reported in 1966 (?) in some British journal concerned with teaching science (or physics) (wasn't it Rutherford who said all science was either physics or stamp-collecting?) Hot water cools faster than cold water (once they are at the same temperature). This is an experimental fact.... I myself did an experiment for a final year undergrad project: Take two beakers (about 2" high), place them in separate 'specially designed containers about a foot across' (empty wine cases) with open tops, and throw the lot into a gigantic cold room at ~-10 Celsius. Fill one beaker with hot water, t'other one with room temp. boiled water. Measure 6 temperatures in each beaker : |____________| | x x| | | | | | x x| | | | x x| \__________/ The experimental fact is that for a given central temperature (say 10 Celsius) the beaker that started off hot had a lower surface temperature. Plenty of comment is possible here... memory of being hot may be resident in the pattern of convection (size? nature?), hence the ability to transfer heat from the body of the liquid to the surface. It is unlikely that dissolved stuff is responsible for the different temperature fields in the two liquids. Incidentally, the temperature measuring devices (my pride and joy) were made by me out of gauge 42 (human hair size) copper-constantan thermocouples. I used sealing wax and string to keep them in place (and clear nail varnish to keep them from shorting out). Anyone looking for a good experimental undergrad project (to set or to do) can try looking at the patterns of convection in such a set up. Interference (light) or coloured tracers...