The Mpemba Effect: Why Hot Water Freezes Faster than Cold! By Dr John Jensen

     I continue my series on amazing things about physics that people may not know. Take the so-called Mpemba effect for example:
  https://en.wikipedia.org/wiki/Mpemba_effect  

     Some folk like to put African people down, belittling their IQ, as we see in the so-called racial realist school, but it was a  poor Tanzanian form 3 school boy, Erasto Mpemba who noticed the effect, previously noted, and variously explained by historical figures such as Aristotle, Francis Bacon and Descartes, that hot water freezes faster than cold. Mpemba, posed this question during his high school education to visiting physicist Dr Denis G. Osborne: “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?”
The teacher and class mates ridiculed him, but Dr Osborne, as a good empirical scientist went and conducted some experiments and confirmed the results. He then published a paper with the lad, rather than keeping it for himself:
  http://iopscience.iop.org/article/10.1088/0031-9120/4/3/312/pdf 

     There are interesting debates about the cause of the Mpemba effect, such as the precipitation out of solutes hypothesis: 
  https://www.eurekalert.org/pub_releases/2006-05/ns-wwf053106.php 

     And supercooling issues:
  http://robot-tag.com/evan/ajp-mpemba.pdf

     But there seems to be no consensus about the real cause of this at present. This example shows that mysterious  science lies as close as your fridge, stove, and water taps!

 

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Tuesday, 24 November 2020
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