Can't stand the heat? Harden up if you want COLD, DELICIOUS BEER

Re: Total, complete & utter bullshit.

Thank you for your comprehensive and rigourous scientific analysis

Re: Total, complete & utter bullshit.

> Total, complete & utter bullshit.

>Don't believe me? Try it for yourself. I did, when I was about six years old. I've demonstrated my results many times in the ensuing nearly five decades.

jake, you didn't prove the Mpemba effect doesn't happen, you only proved that the Mpemba effect doesn't happen in the circumstances you tested.

Variables include respective temperatures of the two (or more) liquid water samples, their size, the shape and size of the containers, the temperature of the freezer, the texture of the test containers (nucleation sites), any difference between the two samples in terms of dissolved solids or gases. It is possible to have observed what you observed, yet still consider the Mpemba effect to be plausible in other circumstances.

There is also ambiguity in the definition of the term, as well; whether it refers to when the water starts to freeze, or to when it is frozen completely.

EDIT: Link added http://phys.org/news188801988.html

Re: Total, complete & utter bullshit.

@jake - I wouldn't go so far as to say "complete and utter bullshit", since clearly the people writing the "Cool?" paper seemed quite convinced with their results. As another commenter posted, there are maybe some situations where the effect works and others where it doesn't.

Anyway, this IS bloody curious, so I've decided to try myself. There's plenty of space in the office freezer, and 2 identical glasses just went into it, one with room temp (approx 20C) water and teh other with water from the coffee machine (approx 80C). Will let you know how it goes

Re: Total, complete & utter bullshit.

To paraphrase the student's original teacher:

Well, all I can say is that that is Jake's physics and not the universal physics.

Re: Total, complete & utter bullshit.

When I was in school this issue was used as an illustration of the problems with the way Aristotle did science. It was said that he wasn't an experimentalist but rather just thought out his experiments and decided that his thoughts were right. Well, he "thought" that hot water cooled faster than cool water so he said that hot water would freeze faster than cold water. Sounds reasonable...until you really think it through.

BUT...

Then several (ten?) years ago I read an article in either Science News or Chemical and Engineering News that showed, when conditions are as they would have been if Aristotle was doing the experiment, that Aristotle was right. Hot (boiling) water DOES freeze faster than cold water.

Here are the conditions:

What would Aristotle have used to hold the water? Likely a wooden bucket, certainly not a glass vessel and probably not a clay pot (though that's possible if you heat the water in the pot), and probably not a metal container either (you'd probably use two identical wooden buckets and pour hot water into one and cold water to the same level in another - or use a third pot to get really identical amounts).

So, boiling water in a wooden bucket. What happens? You lose a considerable amount of the water through evaporation. The wood insulates the water and keeps it warm which keeps it evaporating. By the time the water reaches the temperature of the cool water it has a LOT less mass than the water that initially was cool. From there out the "warm" water gets colder and freezes faster because it has less heat to lose (due to its lesser mass).

So...Aristotle was right - if we use his same equipment.

But if we start with glass or metal containers they transmit the heat much faster and the hot water doesn't have enough time to evaporate much, which means that it takes longer to reach the original temperature of the cold water, which means that it will never catch up. Using our methods cold water does freeze faster than the same amount of hot water.

THAT'S why reproducible experimental methods are so important in science.

I thought that was a pretty cool article! What do you think?

--Michael

Re: a simple thought experiment

You don't even have to go that far. One ice cube tray with boiling water, one with room temperature tap water, side-by-side on the same shelf of the freezer.

The tap water tray freezes faster every time. Seriously, try it.

Re: a simple thought experiment

Uhm, right.

Now, do you see that rabbit and that turtle at the starting line over there?

Re: a simple thought experiment

"Take two identical freezers and add internal camera" - you forgot to add a flashlight :)

"Surely the vessel that started at 60C will have to cool to 20C and meanwhile the one which was at 20C will now be colder. Logically the one which started hotter will always be chasing the cooler one."

If you read the 'Cool?' paper, they suggest a possible mechanism - The water loses most energy from the top surface, and the rate of loss depends on temp difference between water surface and freezer. The hot water is not at a uniform X degrees because there's a convection current that cycles the water. It's possible that 2 beakers with water both have the same average temp of 20 degrees, but the one that went into the freezer at 20 degrees is uniform (so 20 degrees at surface) while the one that started at 60 has a surface temperature of 40 and is mostly 15 elsewhere (so with 40 degrees at surface loses temperature more quickly)

Anyway, my experiment is currently in the freezer, will see how it goes

Re: a simple thought experiment

"Logically the one which started hotter will always be chasing the cooler one."

As I understand it (and I'm only reading the article, not the paper) their hypothesis is that hotter water is effectively a different material than colder water (hysteresis at work). So if the rate of cooling both samples is faster than the rate at which the hotter material "relaxes" into the cooler material, the hotter is not the same stuff even when it reaches the starting temperature of the cooler sample and therefore is not obliged to follow the same cooling curve.

Re: Using logic and not checking against observation was the medieval way to do physics.

Or a drop of sweat.

http://en.wikipedia.org/wiki/Polywater

Re: Using logic and not checking against observation was the medieval way to do physics.

" Using logic and not checking against observation was the medieval way to do physics.

It took several hundred years to break people of that habit."

There's still a whole "field" of science working that way.

:(

But why do they bother? Jake has already proven is a load of bollocks, they just need to listen to him. Well, someone needs to listen to him...someone...please listen.....please....

Re: Nothing to do with

(BTW this is why water-cooled PC systems should be filled with water which has been boiled, then cooled - no dissolved air to bubble out in awkward parts of the loop)

Dunno about yourself, but I use ethylene glycol. Antifreeze, basically. Cheap, widely available, nowhere near as corrosive as water, and tends to already come coloured in a nice shade of blue. You could use food-grade propylene glycol if for some reason you think someone might try to drink the coolant. The term "water cooled" is a misnomer when applied to PC liquid cooling systems. Using water (even the deionized sort) inamongst copper, aluminium and whatever differing metals are in a liquid cooling system is asking for trouble. Or perhaps a practical demonstration of the "sacrificial anode" concept.

See also this link. It may save you a lot of bother and no insignificant amount of money!

Re: Explanation of the Mpemba effect

Nope, they covered that when the second year university students did the experiment. They put a thermal insulator between the beakers and the bottom of the freezer so the hot beaker would still be isolated from the metallic bottom of the freezer. Effect was the same.

As for me, I'm believing the second year uni students over jake.

But Ice Cubes? That's a tricky one.

Right up there with bicycles. (And magnets, if you're a Juggalo.)