I'm a little disappointed that we haven't had a natural -40 here in a couple of years. Neat things start to happen when the temperature drops that low - including that trick where you toss boiling water into the air and it freezes before it can hit the ground (making an interesting "whoosh" sound in the process).
Why would it have to be boiling water? Colder water would freeze faster. (Boiling water has to become colder water on its way to becoming frozen water, assuming it gets that far. So if it doesn't work with colder water, it isn't going to work with boiling water either.) I heard about this trick a couple years ago, but nobody said anything about boiling. So, I tried it in Jan. 2004 when it was -44C, and just got water splattered and frozen on the walkway. :-P Some of it froze in the air, but certainly not all of it.
I think the real 'trick' is fooling people into splashing boiling water on themselves, while you watch. ;-)
I've found that hot water works better than cool water - possibly due to the Mpemba effect. When atara and I conducted the experiment, not only did most of the water freeze in the air, but it emitted an interesting "phoosh!" sound as it froze.
If most of the water froze in the air, then some of it didn't. Without any way to actually quantify the fraction frozen, that's pretty much the same as what I got. I didn't like the water that remained liquid - it stayed frozen on the walkway for a long time.
Mpemba just seems to be a blanket "I don't know why" explanation if hot water happens to freeze faster than cold water in a given situation. If there was an explanation in this case, then I wanted to find it. It is only -17C here, and not -40C, but that didn't stop me from trying this experiment. :-)
I threw several cups of water into the air (not over the walkway this time), alternately at +60C and about +5-+10C. It was obvious that the hot water was making a little snow and the cold water wasn't making much of any. But it was also obvious why. It was because the hot water broke into much smaller droplets in the air than the cold water did. It's the droplet size that has the greatest effect on whether water will freeze before it hits the ground, because smaller droplets fall slower (giving them more time to freeze) and have a greater surface area to volume ratio (so they change in temperature faster).
And the reason the hot water breaks into smaller droplets is because the surface tension and viscosity of water fall with increasing temperature. Wind resistance from throwing the water into the air breaks the hot water into smaller droplets which freeze faster. You could get the cold water to similarly break into droplets just as small if you threw it harder.
But if it is cold enough outside, then both hot and cold water will make snow when you throw them. Colder air is denser (facilitating the breakup into droplets and their suspension in the air), and tends to have a lower relative humidity (because ice crystals can self-nucleate and precipitate out below -30C) which facilitates the droplets cooling off due to evaporation and turns the water vapour into ice crystals also, and the colder air is... well, colder and cools things off faster.
Yeah, that front hit us last night. Very strange weather here yesterday - 34 degrees at O'Hare, while in Kankakee, 70 miles to the south, it was 63 degrees. Thunderstorms, tornado warnings, rain, sleet, frozen rain, and ice. And -30 F wind chills.
Gosh, I love living in Chicago. It's like spring and winter in a blender!
Haha, this will be a great shut-up for my coworkers that whine about the weather. CoWerk: "ZOMG it might get down to -10! MINUS TEN!!!" MrGoat: "Pssh, in MY hometown it's -49 in the wind today." CoWerk: *boggle*
Ayup. Moving here from the coast made me re-evaluate my notion of "cold". This isn't particularly unusual winter weather for this area, but we've been spoilt by near-0 temperatures since early December.
It got really cold here too! Just when I was thinking we were going to get away with a really mild winter. :D Oh well, only about another month til spring. :)
![[identity profile]](https://www.dreamwidth.org/img/silk/identity/openid.png){kind=small}
![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png)
branchandroot
no subject
Date: 2006-02-17 03:04 pm (UTC)no subject
Date: 2006-02-17 07:31 pm (UTC)no subject
Date: 2006-02-17 08:36 pm (UTC)I heard about this trick a couple years ago, but nobody said anything about boiling. So, I tried it in Jan. 2004 when it was -44C, and just got water splattered and frozen on the walkway. :-P Some of it froze in the air, but certainly not all of it.
I think the real 'trick' is fooling people into splashing boiling water on themselves, while you watch. ;-)
no subject
Date: 2006-02-17 08:48 pm (UTC)no subject
Date: 2006-02-17 09:11 pm (UTC)Mpemba effect?
Date: 2006-02-18 01:59 am (UTC)I threw several cups of water into the air (not over the walkway this time), alternately at +60C and about +5-+10C. It was obvious that the hot water was making a little snow and the cold water wasn't making much of any. But it was also obvious why. It was because the hot water broke into much smaller droplets in the air than the cold water did. It's the droplet size that has the greatest effect on whether water will freeze before it hits the ground, because smaller droplets fall slower (giving them more time to freeze) and have a greater surface area to volume ratio (so they change in temperature faster).
And the reason the hot water breaks into smaller droplets is because the surface tension and viscosity of water fall with increasing temperature. Wind resistance from throwing the water into the air breaks the hot water into smaller droplets which freeze faster. You could get the cold water to similarly break into droplets just as small if you threw it harder.
But if it is cold enough outside, then both hot and cold water will make snow when you throw them. Colder air is denser (facilitating the breakup into droplets and their suspension in the air), and tends to have a lower relative humidity (because ice crystals can self-nucleate and precipitate out below -30C) which facilitates the droplets cooling off due to evaporation and turns the water vapour into ice crystals also, and the colder air is... well, colder and cools things off faster.
no subject
Date: 2006-02-17 03:32 pm (UTC)Gosh, I love living in Chicago. It's like spring and winter in a blender!
no subject
Date: 2006-02-17 04:09 pm (UTC)CoWerk: "ZOMG it might get down to -10! MINUS TEN!!!"
MrGoat: "Pssh, in MY hometown it's -49 in the wind today."
CoWerk: *boggle*
no subject
Date: 2006-02-17 07:28 pm (UTC)no subject
Date: 2006-02-17 04:24 pm (UTC)just...Brrrrrrr.....
no subject
Date: 2006-02-18 03:04 am (UTC)