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BOB HIRSHON (host):
The mystery of the Mpemba Effect. I’m Bob Hirshon and this is Science Update.
In the 1960s, while making ice cream, a Tanzanian student named Erasto Mpemba noticed something strange: a hot mixture of milk and sugar froze faster than a cold mixture did— just the opposite of what you’d expect.
BETSY PUGEL (NASA):
His teacher would say “this is Mpemba’s physics, it’s Mpemba’s effect and nobody else’s,” and so they joked with him, make fun of him. And he persisted; I guess they had a lot of ice cream to make in his class.
HIRSHON:
That’s NASA physicist Betsy Pugel. She says Mpemba found the same effect with plain water, and eventually published the odd finding in a scientific journal. Labs around the world replicated his findings, and scientists proposed dozens of possible explanations. But fifty years later, there is still no agreement on what causes the Mpemba Effect. Proof that there are still compelling mysteries to be solved even in a process as commonplace as freezing water. I’m Bob Hirshon, for AAAS, the science society.
Story by Bob Hirshon