Page 20 - Sensor100 Jan '13

The LastWord...
Erasto Mpemba announces RSC competition winner
It is possibly a bit off topic, but have you ever wondered why hot
water freezes faster than cold water?
The phenomenon has apparently been known since Aristotle failed
to explain it and all persons trying to sort it out since have been
defeated.
Erasto Mpemba, a Tanzanian schoolboy
discovered the effect 50 years ago. His
discovery was scorned at first but he
pressed his case with Denis Osborne,
a British physics lecturer in Tanzania,
and they went on to co-write a paper
on the effect published in 1969.
The Royal Society of Chemistry ran a competition for the best
explanation of the effect, now named after Mpemba; they received an
astonishing 22,000 entries. The winner was Nikola Bregovic, re-
search assistant in the field of physical chemistry at the Department
of Chemistry, University of Zagreb, Croatia.
Nikola considered possible explanations as: evaporation of the water;
dissolved gases; heat gradient induced convection; supercooling. His-
conclusion: “this effect is not fully resolved to this day, an indication
that fundamental problems lie underneath it”. So it’s still an open
issue!
Read Nikola’s paper here