People who run barefoot over hot coals (1200 degrees C) look ever so impressive and empowered, but I bet they can't walk over a hotplate at a mere 70 degrees C if it has a layer of oil over it - same insulation / conduction phenomenon.

BTW that wikipedia entry is a blatant attempt to technobamboozle laypeople. "Continuum mechanics", "partial differential equations" and CFD's trouble with turbulent flow has absolutely nothing to do with this; they are mathematical techniques used to describe or solve known heat transfer problems, they are not physical phenomenon that we don't understand.

We had a bet on this at work. The cold cup turned to ice first.

phenomenon my ass!

Absolutely the opposite, mate!

To greg laden: In other words, it is not true that hot freezes before cold … what is true is that people sometimes make poor observations and draw incorrect conclusions.

This experiment had been done carefully by physicists, who discovered the existence of the phenomenon but has yet to understand its cause.

To Doctor Fedora: For what it’s worth, water that’s been heated up AND ALLOWED TO COOL BACK DOWN to a comparable temperature will freeze faster than water of that temperature that was never heated, but that’s only because heating the water removes dissolved gases.

From my understanding, this experiment (conducted by Logan McCarty, a chemist at Harvard University) still used hot water and cold water - not hot water that's allowed to cool back down. His conclusion was that gases were responsible for the effect (i.e. degassed cold water freeze first).

To saen: Read the article and the reference articles. This headline is inaccurate sensationalism, but the point is that VERY hot water (90c-195f) does freeze faster than hot water (80c-175f).

That may be so, but there were a lot of experiments that used hot water (90° C) and cold water (18° C). See: D. Auerbach, Supercooling and the Mpemba effect; when hot water freezes quicker than cold, Am. J. Phys. 63 (1995) 882-885. Link

But I stand by that the Mpemba effect exists, although physicists are unsure of the reason why. Here's an article from Physics World for all you non-believers, and I quote:

In 1995 German physicist David Auerbach at the Max Planck Institute for Fluid Dynamics in Göttingen looked at the role of supercooling in the Mpemba effect. But what he found only made things more complicated. He observed that hot water froze at a higher temperature than cold and therefore in a sense froze "first". However, the cold water took less time to reach its supercooled state and so seemed to freeze "faster". To add to the confusion, earlier researchers had reported the opposite: that initially hot water could be supercooled to lower temperatures than cold water. In 1948 Noah Dorsey of the US National Bureau of Standards argued that this is because heating expels impurity particles that acted as nucleation sites for ice. It has been claimed that this effect leads to hot-water pipes bursting more readily than cold, since deeper supercooling leads to ice fingers that advance right across the pipe and block the flow, while freezing nearer to 0 °C just produces a sheath of ice on the pipe surfaces with an open channel in the centre.

For what it's worth, water that's been heated up AND ALLOWED TO COOL BACK DOWN to a comparable temperature will freeze faster than water of that temperature that was never heated, but that's only because heating the water removes dissolved gases. It also provides you with far less cloudy ice.

Most of the time the explanation for the alleged observation is as simple as the fact that given two exactly identical "quantities" of hot and cold water, there is less hot water than cold water.

In other words, it is not true that hot freezes before cold ... what is true is that people sometimes make poor observations and draw incorrect conclusions.