Is It True that Hot Water Freezes Faster than Cold Water or that Cold Water Boils Faster than Hot Water?

[Curious layman]

Yes and no apparently.

This isn't news or a question, I wasn't sure what to do with it so I stuck it here.

Hot water freezing faster than cold water is a 'fact' I've heard several times now. Searched for an answer and found this.

 Found it an interesting read, Thought I'd post it.

https://www.scientificamerican.com/article/is-it-true-that-hot-water/

 

 

Edited January 20, 2021 by Curious layman

[swansont]

“Mpemba effect” is the search term you want

[Curious layman]

Mpemba effect 

Great story about its origins on wiki. I think the moral of this story is that there are no stupid questions, just stupid answers.

The effect is named after Tanzanian Erasto Mpemba. He described it in 1963 in Form 3 of Magamba Secondary School, Tanganyika, when freezing ice cream mix that was hot in cookery classes and noticing that it froze before the cold mix. He later became a student at Mkwawa Secondary (formerly High) School in Iringa. The headmaster invited Dr. Denis Osborne from the University College in Dar es Salaam to give a lecture on physics. After the lecture, 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, Osborne experimented on the issue back at his workplace and confirmed Mpemba's finding. They published the results together in 1969, while Mpemba was studying at the College of African Wildlife Management.^[9] Mpemba and Osborne describe placing 70 ml (2.5 imp fl oz; 2.4 US fl oz) samples of water in 100 ml (3.5 imp fl oz; 3.4 US fl oz) beakers in the ice box of a domestic refrigerator on a sheet of polystyrene foam. They showed the time for freezing to start was longest with an initial temperature of 25 °C (77 °F) and that it was much less at around 90 °C (194 °F). They ruled out loss of liquid volume by evaporation as a significant factor and the effect of dissolved air. In their setup most heat loss was found to be from the liquid surface.^[9]

Edited January 21, 2021 by Curious layman