Why hot water freezes first than cold water under the same mass and cooling conditions？

What is it about?

" Mpemba effect ", also known as" Mupainmubar effect ", refers to the phenomenon that a slightly hotter liquid freezes first than a slightly cooler one under the same volume, mass and cooling conditions. In 1963, at a high school in Tanzania, there was a junior three student named Mpamba who enjoyed making ice cream with his classmates. They add sugar to boiling fresh milk, let it cool, pour it into a latticed container, and place it in the freezer. One day, Mpemba realized that the freezer room was running short of space. Fearing that the other students would be the first to use it, he quickly added sugar to the boiling milk and sent it to the refrigerator before it cooled down. An hour and a half later, Mpemba noticed something that puzzled him: hot milk freezes faster than cold milk. What's going on here? Confused Mpamba hurriedly ran to ask the teacher, but unfortunately, from junior high school to high school, no teacher took his problem seriously, and some people thought he was absurd and said he was lying. Until one day, Dr. Osborn, the head of the physics department of the University of Dar es Salaam, visited his school, and he seized the opportunity to consult Dr. Osborn. As a result, the doctor not only did not scoff at it, but also took him back to the laboratory to do the experiment. In 1969, Mpamba and Dr. Osborne wrote a paper on this effect and named it "Mpamba effect ". In fact, hot water freezes faster than cold water is a mystery that has been around for thousands of years. Historically, Aristotle, Francis Bacon and Descartes have described the phenomenon in different ways, but none of them has attracted much attention. More than 50 years after the "Mpamba effect " was officially named, scientists have done many experiments and written many papers want to prove the principle behind the phenomenon, but there is still no conclusion. Recently, two physicists Avinash Kumar and John Bechhoefer from simon fraser university, Canada, have bypassed the complexity of water by replacing water molecules with tiny glass beads, developing a method to exhibit the Mpamba effect in a controllable environment, confirming that when two systems with different initial temperatures are cooled to the same temperature, the system with higher initial temperatures can take less time than the system with lower temperatures. The result suggests that the Mpemba effect is not only present in glass beads and water, but is more likely to be present in nature in general.

Featured Image

Photo by Priscilla Du Preez on Unsplash

Photo by Priscilla Du Preez on Unsplash

Why is it important?

This paper makes clear the essence of time through the study of the Mpemba phenomenon and the inverse Mpemba phenomenon.

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