The Mpemba effect is the observation that warmer water sometimes freezes faster than colder water. Although the observation has been verified, there is no single scientific explanation for the effect. Similar behavior was observed by ancient scientists such as Aristotle and early modern scientists such as Francis Bacon and René Descartes. Aristotle's explanation involved an erroneous property he called antiperistasis, defined as "the supposed increase in the intensity of a quality as a result of being surrounded by its contrary quality".
The effect is named for Tanzanian Erasto Mpemba. He first encountered the phenomenon in 1963 in Form 3 of Magamba Secondary School, Tanganyika when freezing ice cream mix that was hot in cookery classes and noticing that they froze before cold mixes. After passing his O-level examinations, he became a student at Mkwawa Secondary (formerly High) School, Iringa, Tanzania. The headmaster invited Dr. Denis G. Osborne from the University College in Dar es Salaam to give a lecture on physics. After the lecture, Erasto Mpemba asked him the question "If you take two similar containers with equal volumes of water, one at 35 °C (95 °F) and the other at 100 °C (212 °F), and put them into a freezer, the one that started at 100 °C (212 °F) freezes first. Why?" only to be ridiculed by his classmates and teacher. After initial consternation, Dr. Osborne experimented on the issue back at his workplace and confirmed Erasto's finding. They published the results together in 1969.
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