Talk:Mpemba effect

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Diagram

I've added a relevant diagram (already available on Wikimedia Commons), and also expanded the Historical section a little, discussing the work of James Black. I know that this has been a contentious topic in the past, but I thought that it was worth gently revisiting; I've tried to be cautious, but might reasonably be accused of over-interpreting Farenheit's contributions in the light of subsequent knowledge; I'm also rather relying on Black's description of Farenheit's work, as my Latin isn't up to scratch. Cluebot archiving removed so that we can have a chat! Klbrain (talk) 12:04, 17 August 2015 (UTC)[reply]

Possible solution

Not sure if this is a solution - I don't understand it enough to add or edit the main article https://medium.com/the-physics-arxiv-blog/why-hot-water-freezes-faster-than-cold-physicists-solve-the-mpemba-effect-d8a2f611e853#.khu4xov6s [[[Special:Contributions/80.4.165.202|80.4.165.202]] (talk) 04:53, 5 May 2016 (UTC)][reply]

The English is so poor in the arxiv article that I find it impossible to evaluate the claims fairly, as it's unclear what they are. My BS detectors go off often.--Elvey^(t•c) 20:42, 26 August 2016 (UTC)[reply]

No one seems to mention this as a possible cause

If you put something hot into a freezer it will switch the thermostat to turn the freezer on. This will cause the temperature inside the freezer to drop and so cause the water to turn to ice more quickly. There is hysteresis on these thermostats so they will reduce the temperature in the freezer to a lower temperature than the set temperature. To do a controlled test you would need to put the hot water ice cube trays cold ones in the same freezer at the same time. Why hasn't someone done this with a camera lens inside the freezer to monitor exactly when each one turns to ice? — Preceding unsigned comment added by Caparn (talk • contribs) 16:49, 9 May 2016 (UTC)[reply]

I would be WP:BOLD and do it myself but I'm not certain I could avoid doing so in a manner that would amount to original research. But if a youtube video from someone whose credentials consist of "some college" can be cited I'll go for it. Mattman00000 (talk) 13:01, 23 June 2016 (UTC)[reply]

interesting temperature

"containers at 35 and 5 °C (95 and 41 °F) to maximize the effect"

This 5 °C is roughly (as if rounded) where liquid water is at maximum density. Freezing from the higher temperature would require less expansion. The density change should also have an effect on entropy. — Preceding unsigned comment added by 97.104.88.146 (talk) 08:26, 22 May 2016 (UTC)[reply]

Improvements

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The article would be improved by a free copy of the chart at http://www.sciencebuddies.org/science-fair-projects/project_ideas/Phys_p032.shtml#background - [1]. (In the US, facts (the main content of the chart) aren't copyrightable.)

Perhaps the article should go into more of the things that would make for a good or bad experiment, and or more or less likely to produce he effect. One of the latter would be assuming that the freezer temperature is stable, while a good experiment might address this by doing the tests at the same time, so any temperature variation would tend to effect the results equally.

I tried to reproduce the effect and didn't find it. Used quarter cups of tap-hot and tap-cold water, in plastic cups in a home freezer. To minimize conduction, I leaned the the cups so they were in contact with the freezer shelf at only a point. I tested all samples at the same time. The cool water froze much sooner than the warm water. Likewise, when professor Osborne first confirmed Mpempa's claim, he minimized conduction, but by placing the samples on a sheet of polystyrene foam. The effect as described implies steps have been taken to minimize conduction, but some efforts to reproduce the effect don't take such steps. (One YouTube video shows beakers being placed directly on a bed of ice cubes!) Looking at the chart noted above, there's no clear optimal set of temperatures to maximize the effect, but it looks like a temperator for the 'cold' water is fairly warm: somewhere around 60 to 80 Celsius is likely optimal.

It's claimed that "the effect has been noted by many scientists throughout history including Aristotle, Francis Bacon and René Descartes." so this should be added if solid sources confirm it. The Aristotle quote is readily verifiable, at least.

This is definitely a case where we should be careful what we say in wikipedia's voice. Extraordinary claims require extraordinary evidence. We've got the 2012 Royal Society of Chemistry competition making it seem quite real, and yet it seems quite fleeting in 2014 - most are saying it's not reproducible --Elvey^(t•c) 20:42, 26 August 2016 (UTC)[reply]

What is 'quantity'?

The article several times refers to the 'quantity' of water without specifying how this is defined. The Mpemba/Osborne experiments appear to have used volume as the measure of quantity. The other obvious measure would be mass (usually measured by weighing in standard conditions). Since the density (mass per unit volume) of water varies with temperature, the two measures are not equivalent, as a unit volume of water at a higher temperature will generally have less mass than the same volume at a lower temperature. Quantitatively the difference is probably too small to explain the alleged phenomena, but it seems desirable to avoid the ambiguity.86.132.140.164 (talk) 13:56, 7 December 2016 (UTC)[reply]

Name

Batholomeo or Bartholomeo ? — Preceding unsigned comment added by 188.238.242.155 (talk) 16:49, 18 December 2016 (UTC)[reply]

Probably with an r. For more information and external sources such as pp 7 and 11 of an FAO report see an old Wikipedia biography of Mpemba--Rumping (talk) 13:29, 16 February 2017 (UTC)[reply]

Talk archives

There are achieves of previous talk at Talk:Mpemba effect/Archives/ 1 and Talk:Mpemba effect/Archives/ 2 but I cannot see a link on these pages --Rumping (talk) 13:29, 16 February 2017 (UTC)[reply]

History

How mpemba effect operates

Nkungwej (talk) 14:52, 24 August 2017 (UTC)[reply]

A personal observation.

When I was a schoolteacher, one of the experiments we did with "special needs" children was to freeze water in a watch glass to make a lens. Demonstrating that it doesn't have to be glass - even ice can make a lens. The teachers'guide suggested that we teachers use near-boiling water for this, because such water contains very few dissolved gases and results in a much "clearer" lens, because in a good quality freezer the water would freeze too quickly for air to dissolve in it.

We were surprised to discover that near-boiling water froze about as quickly as room temperature water. I have no idea whether this is related.

Graph in Article

Isn't there a mistake in the graph? When a substance is changing phase, the temperature of the substances remains constant. In the graph, both the initially hot and initially cold water both show a constant temp, but it's not 0 C!!! Shouldn't that graph be removed?