The Mpemba Effect posted on December 20th, 2008
When University College physicist Denis Osborne visited Mkwawa Secondary School in Iringa, Tanzania, in 1963, he little expected the question he got from student Erasto Mpemba:
“If you take two similar containers with equal volumes of water, one at 35?C and the other at 100?C, and put them into a freezer, the one that started at 100?C freezes first. Why?”
The other students derided Mpemba, but he was right — in cooking class he’d noticed that hot ice cream mixes froze more quickly than cold ones.
Osborne confirmed the effect and shared a publication with Mpemba in 1969. What’s behind “the Mpemba effect” is still something of a mystery — it seems to be a combined result of supercooling, convection, evaporation, and the insulating effect of frost. (If you want to conduct your own experiment, start with containers at 35?C and 5?C.)
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