January 16, 2009

Something you can do with this cold, cold air.

You can throw a cup of boiling water into it!

27 comments:

Original Mike said...

Why is this "bad" science?

I didn't know you had a "bad science" tag. I'm looking forward to perusing it.

Ann Althouse said...

I have a "bad science" tag, which means it can jump into the tags as there's an autocomplete. I meant just plain old "science."

Thanks for alerting me!

Original Mike said...

I like how he cautions to not throw it over the sidewalk. That has the ring of a lesson learned the hard way.

Original George said...

Guys prefer weird science.

AllenS said...

Warning! Do not throw the water into the wind.

EDH said...

I want to know, do I get similar extra credit in science for holding a "point your nipples in the cold air" contest?

peter hoh said...

You can freeze your pants.

Bissage said...
This comment has been removed by the author.
Bissage said...

Now that I've been taking Flomax® . . . that photo gives me an idea . . .

siyeh pass said...

Ain't nature fun! The northern equivalent of frying an egg on a sidewalk.

AllenS said...

Lessons Learned:

When I was a kid, my dad bought a brand new 1955 Chev station wagon. That winter, on a very cold day, for whatever reason, I looked at the door handle and decided to put my tongue on it. You can imagine my surprise when my tongue stuck to it, and the amount of pain when I panicked and pulled it off, not to mention the blood and the sight of part of my tongue still on the door handle. A couple of days later on another very cold day, I was going some where with my mom and she said: "How did you do that with your tongue." And, I said: "Like this." AND I DID IT AGAIN!

David said...

Is it correct that this works with boiling water but not with tepid or cold water?

Could someone please explain why this is so?

Please, Mr. Wizard, please.

Ann Althouse said...

David, follow the link at my link:

It seems likely that there is no one mechanism that explains the Mpemba effect for all circumstances, but that different mechanisms are important under different conditions.

Evaporation -- As the initially warmer water cools to the initial temperature of the initially cooler water, it may lose significant amounts of water to evaporation. The reduced mass will make it easier for the water to cool and freeze. Then the initially warmer water can freeze before the initially cooler water, but will make less ice. Theoretical calculations have shown that evaporation can explain the Mpemba effect if you assume that the water loses heat solely through evaporation [11]. This explanation is solid, intuitive, and evaporation is undoubtedly important in most situations. However, it is not the only mechanism. Evaporation cannot explain experiments that were done in closed containers, where no mass was lost to evaporation [12]. And many scientists have claimed that evaporation alone is insufficient to explain their results [5,9,12].

Dissolved Gasses -- Hot water can hold less dissolved gas than cold water, and large amounts of gas escape upon boiling. So the initially warmer water may have less dissolved gas than the initially cooler water. It has been speculated that this changes the properties of the water in some way, perhaps making it easier to develop convection currents (and thus making it easier to cool), or decreasing the amount of heat required to freeze a unit mass of water, or changing the boiling point. There are some experiments that favor this explanation [10,14], but no supporting theoretical calculations.

Convection -- As the water cools it will eventually develop convection currents and a non-uniform temperature distribution. At most temperatures, density decreases with increasing temperature, and so the surface of the water will be warmer than the bottom -- this has been called a "hot top." Now if the water loses heat primarily through the surface, then water with a "hot top" will lose heat faster than we would expect based on its average temperature. When the initially warmer water has cooled to an average temperature the same as the initial temperature of the initially cooler water, it will have a "hot top", and thus its rate of cooling will be faster than the rate of cooling of the initially cooler water at the same average temperature. Got all that? You might want to read this paragraph again, paying careful distinction to the difference between initial temperature, average temperature, and temperature. While experiments have seen the "hot top", and related convection currents, it is unknown whether convection can by itself explain the Mpemba effect.

Surroundings -- A final difference between the cooling of the two containers relates not to the water itself, but to the surrounding environment. The initially warmer water may change the environment around it in some complex fashion, and thus affect the cooling process. For example, if the container is sitting on a layer of frost which conducts heat poorly, the hot water may melt that layer of frost, and thus establish a better cooling system in the long run. Obviously explanations like this are not very general, since most experiments are not done with containers sitting on layers of frost.


That's a discussion of 2 containers of water. Obviously, hurling the water into the air creates some new conditions.

Dust Bunny Queen said...

Very interesting and fun. This part of the linked article was also very cool

"While this phenomenon has been known for centuries, and was described by Aristotle, Bacon, and Descartes [1-3], it was not introduced to the modern scientific community until 1969, by a Tanzanian high school student named Mpemba"

A Tanzanian high school student....a very smart, curious and scientific minded student. Wonderful! Talent can arise anywhere at anytime if it has the opportunity. Think how much knowledge has been lost, now and through the ages, because the opportune circumstances weren't there for the "cream to rise to the top". If Einstein became a bookkeeper who never made his theories public. If Newton under the tree just ate the apple and went home for a nap.

chuck b. said...

Why don't you do some things like this for us, Althouse? There hasn't been any new photography in forever.

It's 65 deg F and sunny in California. Your frozen landscape is fresh and exotic. Here we are now. Entertain us.

dbp said...

The Mpemba effect is fascinating, but I think it has little to do with throwing hot water into the air when it is really cold out.

Like Althouse said, "That's a discussion of 2 containers of water. Obviously, hurling the water into the air creates some new conditions."

When you throw water up into the air, three things can happen: 1. Some will evaporate (heat of vaporization about 540 Calories/gram). 2. Some will freeze, (heat of fusion about 80 Calories/gram) 3. There might be some that remains liquid, but just gets colder on the way down, 1 Calorie per degree per gram.

As you can see from the numbers given, the temperature of the water is pretty minor compared with the amount of energy transfer from evaporation and freezing.

What I suspect is that hot water spreads more evenly when flung into the air, due to weaker surface tension in hot water. Smaller droplets allow much quicker transfer of heat into the air.

Dust Bunny Queen said...

It's 65 deg F and sunny in California. Your frozen landscape is fresh and exotic

Speak for yourself, Chuck. Its 10 degrees here in "California" and might warm up to above freezing today. The snow has turned to a solid pack of ice. I think we have a glacier forming in our shady driveway.

I have to laugh when people make a big deal about the -12 degrees in the midwest. Over the Christmas vacation we were at -18 and a high of 8 during the day. Where was the big news story about us? LOL

Perspective :-)

Original Mike said...

Where was the big news story about us?

It can't always be about California, DBQ. We hear more than enough about you as it is. There are other parts of the country. ;-)

Dust Bunny Queen said...
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Dust Bunny Queen said...

It can't always be about California, DBQ. We hear more than enough about you as it is. There are other parts of the country. ;-)

Hee hee. Agreed. Actually, I like the cold. It keeps people from the Bay Area and LA area from moving here. (It is quite lovely in the spring, summer and fall however. Elevation 3600 ft.)

I bet the people in Montana feel the same way about California immigrants.

Speaking of cold air and science. We had wispy freezing fog yesterday morning on the river below us and the sunrise through the frozen crystals was spectacular and strange looking.

*Freudian slip spelling error fixed

Tibore said...

Ohmigod! Thanks to the professor, I have completely and utterly wrecked productivity where I work at by spamming that link out. The microwave's getting the most pre-lunch use I have ever seen. :)

There's a big picture window that's been transformed into one of the biggest work "stages" for performance art in recent knowledge. We're now wondering how to heat quantities of water bigger than a cup with the office materials we have, and how to get it even higher into the air.

Man... Fridays rule. :D

Original Mike said...

Actually, I like the cold. It keeps people from the Bay Area and LA area from moving here.

Me, too. Too many people in Wisconsin, already.

chuck b. said...

"Actually, I like the cold. It keeps people from the Bay Area and LA area from moving here."

That's not all that keeps people from moving there.

Chip Ahoy said...

This is very interesting. I tried this once in my freezer and cold water clearly won. This made me feel like a failure because I wanted hot water to win, because I prefer living in an insane universe.

Still, though, this explanation of the Mpemba effect, which amounts to three iffy, sometimes, under certain conditions, too many variables to account for them all, not always duplicatable because of things we still don't know about, fragmentary could-be, maybe, perhaps, sometimes, I think, uncertain explanations, is the worst scientific explanation I've ever heard. Read three times now in fifteen minutes, twice over there and once here, and I still don't have a good answer!

Makes me want to try it. Can't wait for a super freezy day.

Chip Ahoy said...
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Chip Ahoy said...

I put a large tub of sourdough sponge on the balcony in sub-freezing temperature. I kept a rapid-read thermometer at the door and took its temperature regularly, checking to make sure it wouldn't freeze. The wet sponge was remarkably stable. This caused me to conclude the bubbles in the sponge made the sourdough behave like a piece of insulation. That makes me weight the diffused air theory more heavily.

[changed "it's" to "its" up there ^^^]

Original Mike said...

Madison's weather forecast for tonight.

Bitterly cold. Not as cold. Increasing clouds. Chance of light snow and patchy light freezing drizzle after midnight. Lows around 7 below. South winds 5 to 15 mph. Chance of precipitation 50 percent. Wind chill readings 15 below to 25 below zero.

Freezing drizzle?