Re: Starving people refuse to eat food aid
Thomas Womack
Keith F. Lynch <k...@KeithLynch.net> wrote:
> Much further north, I figured it would stay below
> freezing the whole winter, and, while there may be plenty of snow,
> there would be little or no slick ice.
You have to be a lot further north for that; Yellowknife manages to be
below zero from November to March, but Yellowknife is 62 north and
many miles from the sea. Novosibirsk has been known to be above zero
in December, though seems to be comfortably sub-zero for all January.
Snow over a hard surface (say, sidewalk or previous ice) will of
course get trampled into ice pretty quickly; I know from personal
experience that Montreal in January is not devoid of slick ice.
Tom
Joyce Haslam
> Keith F. Lynch wrote:
>> Much further north, I figured it would stay below freezing the whole
>> winter, and, while there may be plenty of snow, there would be little
>> or no slick ice.
> You have to be a lot further north for that; Yellowknife manages to be
> below zero from November to March, but Yellowknife is 62 north and many
> miles from the sea. Novosibirsk has been known to be above zero in
> December, though seems to be comfortably sub-zero for all January.
>
> Snow over a hard surface (say, sidewalk or previous ice) will of course
> get trampled into ice pretty quickly; I know from personal experience
> that Montreal in January is not devoid of slick ice.
And you always get the occasional householder who shovels away the snow
and then washes the sidewalk with hot water - which freezes skating-rink
smooth.
--
Joyce.
cryptoguy
wrote:
> In article <hfmuu8$in...@reader1.panix.com>,
Apropos the snow->ice transition, and the ice skating topic, I wonder
to what extent we're factoring friction into the equation. Any skier
or skater knows that there is a certain stick/slip factor in moving on
frozen water of any kind. A stationary skier or skater has to use a
bit of extra force to start from a dead stop.
Avalanches take place in very cold snow, but when the avalanche ends,
there is enough liquid water in the system that the snow re-freezes
into a solid mass. I've seen this myself in the Alps, skiing across
avalanche debris is like trying to cross the banks left behind by a
snowplow; not fun. It's also a serious issue for people caught
snowslides; at the end, the snow re-freezes around them like concrete,
trapping them.
Making snowballs also comes to mind - with enough pressure, you can
make snowballs from any type of snow (the colder, the more difficult).
Regardless of the phase diagram, these are real phenomena. They
suggest to me that real, dynamic systems are more complex than the
static lab models.
pt
Keith F. Lynch
> Avalanches take place in very cold snow, but when the avalanche
> ends, there is enough liquid water in the system that the snow
> re-freezes into a solid mass.
How much heat is generated by the avalanche? All that gravitational
potential energy turns into kinetic energy then into heat. That might
suffice to do a lot of melting.
--
Keith F. Lynch - http://keithlynch.net/
Please see http://keithlynch.net/email.html before emailing me.
Strobe
wrote:
That also happens naturally - it's a normal hazard here in NYC.
While the air temp is below freezing, insolation can melt banks of shovelled
snow and the melt water then runs across a sunlit sidewalk.
The sun sets, or a building shadow moves across - instant black ice!
erilar
Strobe <Str...@nyc.Beep!Beep!.com> wrote:
> While the air temp is below freezing, insolation can melt banks of shovelled
> snow and the melt water then runs across a sunlit sidewalk.
> The sun sets, or a building shadow moves across - instant black ice!
Which is why I snarl at people who cheerfully talk about "what a nice
warm day we're having" after snow has piled up. Weather forecasters are
the worst. Don't any of them realize what's going to happen as soon as
the temperature goes back to winter normal?
--
Erilar, biblioholic medievalist
Richard Casady
<k...@KeithLynch.net> wrote:
>How much heat is generated by the avalanche? All that gravitational
>potential energy turns into kinetic energy then into heat. That might
>suffice to do a lot of melting.
Why don't you take a few seconds and push a few buttons on your
calculator. 68 BTU per pound per mile. The latent heat of fusion of
water is left as an exercise for the reader mostly because I cant
remember it. The heat of evaporation is 1073 BTU per pound, but
whatever.
Casady
Thomas Prufer
wrote:
>The latent heat of fusion of
>water is left as an exercise for the reader mostly because I cant
>remember it. The heat of evaporation is 1073 BTU per pound, but
>whatever.
There was a documentary on avalanches t'other day, and they mentioned that the
density of the snow that had poured into a small town was 400 kg/m^3 afterwards,
i.e. 0.4 times the density of water.
Thomas Prufer