Cool? A paper by Erasto Mpemba and Denis Osborne, 1969

A Puzzling Phenomenon: The Story Behind the Mpemba Effect

In the world of science, a single curious question from a student can sometimes challenge long-held beliefs. This is the story of Erasto Mpemba, a Tanzanian student whose observation in 1963 sparked decades of scientific debate, leading to a paper that bears his name.

The phenomenon, now known as the Mpemba effect, is the counterintuitive observation that under certain conditions, hot water can freeze faster than cold water. Mpemba first noticed this while making ice cream at his school. He was told to wait for the boiled milk mixture to cool before putting it in the freezer, but on a whim, he placed his hot mixture in the freezer tray. To his surprise, it froze before the cold mixtures of his classmates.

When he asked his physics teachers about this, he was met with ridicule. "That is Mpemba's physics," they would say, dismissing his observation. But Mpemba persisted. A few years later, while attending a lecture by Dr. Denis Osborne, a visiting physics professor, he bravely posed the question again. Intrigued, Dr. Osborne conducted his own experiments back at the University College in Dar es Salaam and confirmed Mpemba's finding.

In 1969, their joint paper, titled "Cool?", was published in the journal Physics Education, formally introducing the Mpemba effect to the scientific community. The paper detailed their experiments and highlighted the importance of a student's curiosity in scientific discovery.

While the effect has been observed throughout history by figures like Aristotle and Francis Bacon, it was Mpemba's perseverance and Dr. Osborne's willingness to listen that brought it to modern scientific attention. Even today, the precise reasons behind the Mpemba effect are still a topic of debate among physicists, with various theories proposed, including evaporation, convection, and supercooling.

The story of Erasto Mpemba is a powerful reminder that observation and curiosity are at the heart of science, and that even the most simple, unexpected questions can lead to profound discoveries.

You can read the original paper by Erasto Mpemba and Denis Osborne here: www.rsc.org/.../Cool-Mpemba-Osborne1969_tcm...