The Great "Wind Chill Factor" Hoax
Richard Penny
: On a calm night, the air in the engine compartment will slow the heat
: loss (much like the air in a double-pane window). With the wind
: blowing, air exchanges will occur, allowing the warmer air in the
: engine compartment to be replaced by colder (ambient temperature) air.
: In reference to the original question, the effects of wind chill
: effect living flesh (as a function of heat loss versus internal
: temperature maintenance).
: It's 40 degrees and raining, and you're driving along at 45 miles an
: hour. You choose to make like your dog and hang your head out the
: window. It gets cold real fast because your "Wind Chill" (40 degrees @
: 45 mph) would be about 10 degrees above zero. That's what it feels
: like on your face, based on the heat loss due to the ambient
: temperature + the wind.
: But if wind chill impacted inantimate objects in the same way, the
: rain would freeze on your windshield. But it doesn't because the
: actual temperature is above freezing. Wind Chill is, in effect, an
: illusion.
: An IMPORTANT illusion, nonetheless. If the temperature outside is 20
: degrees, you may decide to just wear a winter jacket and gloves. But
: with a wind of 35 mph, you have a wind chill of 20 below. Better get
: your scarf, knit cap, heavier mittens, etc. etc. etc.
Is frostbite an illusion, too?
As it happens, wind will increase the rate of heat loss from inantimate
objects just as it does from antimate ones.
There are four mechanisms whereby objects lose heat: convection,
radiation, conduction, and evaporation.
Wind increases the rate of both convective and evaporative heat loss.
---------------------------------------------------------------------------
Richard Penny email: rikp...@cybergate.com
---------------------------------------------------------------------------
Robert Muller
30 seconds before freezing.
Joshua P. Weage
: : hour. You choose to make like your dog and hang your head out the
: : window. It gets cold real fast because your "Wind Chill" (40 degrees @
: : 45 mph) would be about 10 degrees above zero. That's what it feels
: : like on your face, based on the heat loss due to the ambient
: : temperature + the wind.
: : But if wind chill impacted inantimate objects in the same way, the
: : rain would freeze on your windshield. But it doesn't because the
: : actual temperature is above freezing. Wind Chill is, in effect, an
: : illusion.
I guess your point is that the wind chill doesn't
reduce the ambient temperature, just increases heat loss.
That is just about true. Evaporation, however, will reduce
the surface temp to below ambient temperature.
Josh
--
----------------------------------------------------------------
-- Joshua Weage E-Mail : we...@mtu.edu --
-- Third Year ME Student & CAEL Partner --
-- Check out my homepage @ http://www.me.mtu.edu/~weage/ --
-- "Together we will rule the universe, all by myself" --
-- -- Tom Servo Mystery Science Theater 3000 --
David Paul
>: It's 40 degrees and raining, and you're driving along at 45 miles an
>: hour. You choose to make like your dog and hang your head out the
>: window. It gets cold real fast because your "Wind Chill" (40 degrees @
>: 45 mph) would be about 10 degrees above zero. That's what it feels
>: like on your face, based on the heat loss due to the ambient
>: temperature + the wind.
>: But if wind chill impacted inantimate objects in the same way, the
>: rain would freeze on your windshield. But it doesn't because the
>: actual temperature is above freezing. Wind Chill is, in effect, an
>: illusion.
No, your definition fails to take into consideration the temperature
difference. If an object is the same temperature as the surrounding air, then
increasing the velocity of the wind will not lower the temperature of the
object. If there is a difference in temperature, then increasing wind
velocity increaces the RATE of temperature change for the object.
And just to confuse matters more, if rain were hitting the windshield the
speed of the wind could accelerate the evaporation process, so it is quite
possible that the tempreature of the windshield could actually be lower than
the ambient air temperature.
Richard Penny
: : But if wind chill impacted inantimate objects in the same way, the
: : rain would freeze on your windshield. But it doesn't because the
: : actual temperature is above freezing. Wind Chill is, in effect, an
: : illusion.
As I stated in a previous post, wind chill is neither a hoax nor an
illusion. Nor is the windchill index merely a psychophysical scaling
reflecting perceived skin temperature under conditions of wind. Rather,
wind chill is a physical phenomenon which affects the rate of cooling of
all bodies, both antimate and inantimate. What follows are some quotes
from several authoritative references.
---------
Guyton, Arthur C. and Hall, John E. _Textbook of Medical Physiology_. 9th
Ed. W.B. Saunders, Philadelphia, Pennsylvania: 1996, p. 913.
Unit XIII: Metabolism and Temperature Regulation
"Conduction. As shown in Fig. 73-4, only minute quantities of heat
are normally lost from the body by direct conduction from the surface of
the body to other objects, such as a chair or a bed. On the other hand,
loss of heat by _conduction to air_ does represent a sizable proportion of
the body's heat loss (about 15%) even under normal conditions. It will be
recalled that heat is actually the kinetic energy of molecular motion, and
the molecules of the skin are constantly undergoing vibratory motion. Much
of the energy of this motion can be transferred to the air if the air is
colder than the skin, thus increasing the velocity of motion of air
molecules. Once the temperature of the air immediately adjacent to the
skin equals the temperature of the skin, no further loss of heat occurs
because now an equal amount of heat is conducted from the air to the body.
Therefore, conduction of heat from the body to the air is self-limited
_unless the heated air moves away from the skin_, so that new unheated air
is continually brought in contact witht he skin, a process called air
convection.
Convection. The removal of heat from the body by convection air
currents is commonly called heat loss by convection. Actually, the heat
must first be _conducted_ to the air and then carried away by convection
currents.
A small amount of convection almost always occurs around the body
because of the tendency for the air adjacent to the skin to rise as it
becomes heated. Therefore, a nude person seated in a comfortable room
without gross air movement still loses about 15% of his or her heat by
conduction to the air and then by air convection away from the body.
Cooling Effect of Wind. While the body is exposed to wind, the
layer of air immediately adjacent to the skin is replaced by new air much
more rapidly than normally and heat loss by convection increases
accordingly. The cooling effect of wind at low velocities is about
proportional to the _square root of the wind velocity_. For instance, a
wind of 4 miles per hour is about twice as effective for cooling as a wind
of 1 mile per hour."
"Figure 73-4 Mechanisms of Heat Loss from the body. (room temperature).
Radiation (heat waves) 60%
Conduction to air 15%
Evaporation 22%
Conduction to Objects 3%"
------
West, John B. _Best and Taylor's Physiological Basis of Medical Practice_.
12th Ed. Williams and Wilkins, Baltimore: 1991, p. 1064.
"Convection is promoted by movement of air across body surfaces.
For any given air temperature, heat losses from a naked body increase with
the square of the wind velocity up to 60 mph, beyond this there is little
further increase because of limitations on heat movement through tissues.
Chill factor in cold wether winds can be appreciated by the rapidity of
convection heat loss, with the wind velocity being squared."
____
Note that Guyton and Hall use a square root of the velocity as the wind
chill factor, and West uses the square of the velocity. I expect that
Guyton and Hall are correct. It seems unlikely that a 30 mph wind would
cause a 900-fold increase in cooling rate.
------
Reifsnyder, William E._ Weathering the Wilderness: The Sierra Club Guide
to Practical Meteorology_. Sierra Club Books: San Francisco, 1980. pp.
77-78.
"Windchill. When the air is colder than the skin, heat is lost from
the skin by convection. The rate of heat loss is proportional to the rate
of airflow over the skin. That is, the harder the wind blows, the greater
the rate of heat loss and the colder the skin will be. Because our
sensation of temperature depends in large degee on skin temperature, we
expect to perceive the same degree of comfort at various combinations of
wind and air temperature to produce the same heat loss from the body.
The so-called windchill index or (preferably) windchill
temperature was developed by Paul Siple during Antarctic expeditions. It
is defined as the temperature that essentially still air (about 3 mph or
less) would have in order to produce the same heat loss from the skin
exposed to a given combination of wind and temperature. For example, at an
air temperature of 20 degrees F and a wind speed of 15 mph, the windchill
temperature would be -13 degrees F. That is, heat loss from the face or a
bare arm exposed to these conditions would be approximately equal to that
from exposure to a 3 mph wind when the air temperature was -13F."
MC Hamster
me introduce this thought which has probably come up earlier.
I see the Wind Chill Factor as a hoax because it bases itself on an
assumption that we should use temperature with NO wind velocity as our
starting conditions and then reduce that apparent temperature to account
for the effects of wind. This would be fine if we usually experience
conditions of zero wind velocity... but of course we don't. Thus, most
times it is, say, 20 degrees outside there is also a wind of, say, 10
mph... thus when we experience the real world conditions of 20 degrees the
wind chill then is lower. The effect is "wind chill inflation", i.e.,
making it seem much colder than it really is for dramatic effect on the
weather reports on TV. When we grew up, 20 degrees wasn't that cold; now,
when it is 20 degrees outside, the concommitant wind chill is usually, oh,
-10 and my kids run around and talk about how bad it is outside and how
it's too cold to take out the garbage, etc....
MY SOLUTION IS to re-paramatize the wind chills to factor in an average
wind speed we usually experience. Thus, if the actual weather conditions
should be, say, 20 degrees and there happens to be almost zero wind
outside, the reported "wind chill factor" would be HIGHER than 20 degrees.
There is absolutely no reason we shouldn't CELEBRATE days when we are
lucky enough to have no wind in the wintertime... is there??
M C Hamster @ aol.com (aka David...@aol.com)
____________________________________________
o//~~ Big Wheel Keep on Turnin'.. Proud Mary Keep on Burnin'~~//o :
Creedence
rockdog
>
>: HappyBoy (paul...@borg.com) wrote:
>
>: : But if wind chill impacted inantimate objects in the same way, the
>: : rain would freeze on your windshield. But it doesn't because the
>: : actual temperature is above freezing. Wind Chill is, in effect, an
>: : illusion.
>
>As I stated in a previous post, wind chill is neither a hoax nor an
>illusion.
So what is your point? What "happyboy" said is absolutely true. Only the
*rate* of chilling changes with wind chill factored in. If it's 40 degrees
out then the rain *will not* freeze to the windshield in his example.
Richard Penny
: So what is your point? What "happyboy" said is absolutely true. Only the
: *rate* of chilling changes with wind chill factored in. If it's 40 degrees
: out then the rain *will not* freeze to the windshield in his example.
Happyboy's example was correct, but misapplied. The thesis that Happyboy
used it to support is absolutely false. Windchill affects all objects,
antimate and inantimate in the same way. He stated the opposite. Happyboy
also stated that windchill is an illusion. It is not; rather, it is a
physical process.
His befuddlement on this point is reflected by the less than apt freezing
rainwater example. Yes, windchill will not cause normally cause rainwater
to freeze on a windshield when the ambient temperature is above freezing.
But then neither will it normally cause rainwater to freeze on one's skin.
You see, cars and people are affected by windchill in the same regard.
Suppose for example, your car is at rest at in an environment where the
ambient temperature is 30 degrees and there is no wind. Let's suppose that
this car has a non-thermostatically controlled heater, and that a setting
of "one" is adequate to keep the interior of the car warm under the
initial set of conditions. Now suppose one were to drive that car forward
at 30 mph. The exterior windchill temperature would drop to -9 degrees F.
The rate of convective heat loss from the car would increase, and a
passenger might discover that he had to turn the heat setting to "two" or
"three" in order to maintain a comfortable equilibrium temperature within
the passenger compartment of the automobile.
HappyBoy
>rockdog (roc...@indra.com) wrote:
First, if it appeared that I was in the "wind chill is an illusion"
camp, then I goofed. Wind chill is real, in that moving wind can
increase heat loss to the point of producing something of an
"illusionary" temperature (the wind chill temperature).
What I wanted to debunk was the idea that the wind chill temperature
was an actual temperature.
Going back to my original example - driving in a car at 45 mph in 40
degree weather with light rain falling. Sticking your head out the
window would make your face quite cold, because, with the wind chill
factored in, the heat loss would be the same as if your head were
exposed to ten degree calm air. But it's not the actual temperature
experienced by objects exposed to the wind. The windshield (which is
also experiencing a 45 mph wind at 40 degrees ambient temperature)
would remain above freezing, so the rain would not freeze on the
winshield.
Lets change the example a little. Same temp and speed, except now
you're driving a dune buggy with no winshield, and will be driving it
like that for approximately eight hours straight. There will be a
light rain the whole way. Oh -- you also are only wearing a light
jacket - after all, it's only 40 degrees.
So for eight solid hours, you'll be exposed to a relative wind chill
of ten degrees above. And rain. Ick. Will there be icicles in your
hair or beard? Shouldn't be - ambient air temperature is above
freezing. Will you suffer frostbite? Probably not, since that
represents body portions dropping below freezing and the air
temperature is 40 degrees. Will you suffer hypothermia? Most
definitely, since in this example you're dressed for a chilly autumn
temperature (40 degrees) and not an arctic temperature (10 degrees).
Richard, I hate to question your example since you have supplied a
number of well-informed references to back up the conclusion that wind
chill has an effect on inanimate objects. But I have a question about
your car heater example above.
A car's heater works by drawing outside air in past a heater core. The
temperature of the air is regulated by mixing air moving past the
heater core with outside air which bypasses the core.
In moving at highway speeds at a setting of "one," the cooler
temperatures in the car would be the result of the cold "bypass" air
coming in at a greater rate when the car is moving than when the car
is still. Consequently, the interior is colder not due to wind chill
outside the car but because the air being delivered out the heater
vents isn't as warm as original.
The point that some people forget about this is that there is more
than just temperature to determining if you will feel "hot" or "cold."
Wind chill and heat index (a heat & humidity calculation) are attempts
to take those extra factors into account. Last summer, during a
particularly oppressive heat wave, belittled a NYC disc jockey who had
the nerve to say "It's 101 degrees. But with the humidity, it feels
like 160." To Letterman, that high a temperature was impossible, and
therefore, saying it was 160 was asinine.
Of course, he said that from inside the confines of the ever-frosty Ed
Sullivan Theatre.
>>>> HappyBoy
paul...@borg.com
MC Hamster
>
> OK, so let's reparameterize our highway speeds, too, to take into
>account the normal driving speeds we experience.....
> Do you see the point? To make sense, a scale or set of standards
>needs an absolute. Rather than reparameterizing -- a process which
>would give you a different scale for every region with different average
>winds -- just go outside wen there is no wind and feel the temperature on
>your bare skin.... i.e., reparameterize yourself; leave the scale alone.
Oh, I'd only have one average wind speed figured into the calculation --
of course I wouldn't have different wind speeds for each region. Yeah, it
would be perpetually chillier then on the heaths of Devon than in some
tamer locale, but this needs to be a workable system. We could pick, um,
10 mph.
My posting is simply a backlash against the histrionics that the wind
chill produces in TV meteorologists which are then repeated, like shock
waves through the populace ("it will be wind chills of 25 below tonight!!!
Brutally cold out there!!") when the TRUTH is that it is only 15 above
and, yeah, a little windy but it is USUALLY a little windy -- whattya
want, anyway? The Garden of Eden?? Perhaps at some future date when
these wind chills have become pervasive and we all know that it ain't
really all that cold out until we reach wind chills of, say 35 below, then
I'll feel better about all this.
I used to walk four miles to school when I was a kid too.
the ROYster-Meister
On 12 Feb 1996, MC Hamster wrote:
> I am stunned this thread is still going, after months I think... but let
> me introduce this thought which has probably come up earlier.
>
> I see the Wind Chill Factor as a hoax because it bases itself on an
> assumption that we should use temperature with NO wind velocity as our
> starting conditions and then reduce that apparent temperature to account
> for the effects of wind. This would be fine if we usually experience
> conditions of zero wind velocity... but of course we don't. Thus, most
> times it is, say, 20 degrees outside there is also a wind of, say, 10
> mph... thus when we experience the real world conditions of 20 degrees the
> wind chill then is lower. The effect is "wind chill inflation", i.e.,
> making it seem much colder than it really is for dramatic effect on the
> weather reports on TV. When we grew up, 20 degrees wasn't that cold; now,
> when it is 20 degrees outside, the concommitant wind chill is usually, oh,
> -10 and my kids run around and talk about how bad it is outside and how
> it's too cold to take out the garbage, etc....
>
> MY SOLUTION IS to re-paramatize the wind chills to factor in an average
> wind speed we usually experience. Thus, if the actual weather conditions
> should be, say, 20 degrees and there happens to be almost zero wind
> outside, the reported "wind chill factor" would be HIGHER than 20 degrees.
> There is absolutely no reason we shouldn't CELEBRATE days when we are
> lucky enough to have no wind in the wintertime... is there??
>
>
OK, so let's reparameterize our highway speeds, too, to take into
account the normal driving speeds we experience.....
Do you see the point? To make sense, a scale or set of standards
needs and absolute. Rather than reparameterizing -- a process which
would give you a different scale for every region with different average
winds -- just go outside wen there is no wind and feel the temperature on
your bare skin.... i.e., reparameterize yourself; leave the scale alone.
------------------------------------------------------------------------------
-- the ROYster-meister + wil...@Peak.org --
one of God's >peculiar< people
"But you are a chosen race, a royal priesthood, God's peculiar people."
-- the Apostle Peter (KJV)
------------------------------------------------------------------------------
Frank Crary
Greg Diamond <gdia...@gwis2.circ.gwu.edu> wrote:
>>My posting is simply a backlash against the histrionics that the wind
>>chill produces in TV meteorologists which are then repeated, like shock
>>waves through the populace ("it will be wind chills of 25 below tonight!!!
>> Brutally cold out there!!") when the TRUTH is that it is only 15 above
>>and, yeah, a little windy but it is USUALLY a little windy
>So, are you saying that the subjective feeling of (say) being in 15
>degree weather with a 20 mph wind *is not* similar in terms of felt
>coldness to being in -25 degree weather with no wind? Or are you saying
>that the physiological effects (frostbite, etc.) are not the same? Or
>are you saying that the scale is reasonably apt, but somehow is
>miscalibrated (and if so, what is your evidence for this)?
I think he's saying that the way it's usually reported is misleading.
The weather reports usually say something like, "It's 40 deg, but
with the wind chill it feels like 15 deg." When people hear that,
they probably think of the last time they were outside in 15 deg
weather, not the last time they were outside in 15 deg weather
_and_ no wind. So they get the wrong impression. Relative to
personal experience, it should be compared to a temperature
with moderate or typical winds and wind chill; that's what
people think when they hear, "it feels like x deg." But that's
not really a practical way to state the temperature or wind
chill. (What's a typical wind?)
Frank Crary
CU Boulder
Mary Shafer
took a course on transport phenomena, it's possible for things to
freeze when the air temperature is a few degrees above freezing. This
only happens on clear, calm nights with lowish humidity, when the
object can get colder than the air by black-body radiation.
Fruit routinely is in danger of this, which is why citrus groves used
to have smudge pots. The thick smoke prevented the loss of heat to
space by reflecting the radiated energy back to the fruit. As I
recall from the example problem we worked out, the air temperature can
be as high as 36 deg F and the fruit will still freeze. (They stopped
using smudge pots because they really polluted and now they use big
fans.)
This same phenomenon of radiating heat is the reason that deserts have
hot days (lots of incoming radiation) and cold nights (lots of
outgoing radiation). Here where I live in the Southern California
High Desert we usually have at least 30-deg F swings between the high
and the low all year. When the wind blows or it's cloudy, this drops
to only a few degrees sometimes.
--
Mary Shafer DoD #0362 KotFR sha...@ursa-major.spdcc.com
URL http://www.dfrc.nasa.gov/People/Shafer/mary.html
Some days it don't come easy/And some days it don't come hard
Some days it don't come at all/And these are the days that never end....
Greg Diamond
MC Hamster <mcha...@aol.com> wrote:
>My posting is simply a backlash against the histrionics that the wind
>chill produces in TV meteorologists which are then repeated, like shock
>waves through the populace ("it will be wind chills of 25 below tonight!!!
> Brutally cold out there!!") when the TRUTH is that it is only 15 above
>and, yeah, a little windy but it is USUALLY a little windy
So, are you saying that the subjective feeling of (say) being in 15
degree weather with a 20 mph wind *is not* similar in terms of felt
coldness to being in -25 degree weather with no wind? Or are you saying
that the physiological effects (frostbite, etc.) are not the same? Or
are you saying that the scale is reasonably apt, but somehow is
miscalibrated (and if so, what is your evidence for this)?
Or are you saying that all of the above assertions may in fact be true,
but you just don't like it?
--
<><><> Godwin's Law: comparing the behavior of political actors to
Greg<> that of the Nazis stifles communication and is prohibited.
<>/\<> Diamond's Proviso: if Pat Buchanan wins the New Hampshire
<>\/<> primary, Godwin's Law is suspended for six months, minimum.
Brad Whitehurst
>Just to add a little more confusion to this issue, and prove that I
>took a course on transport phenomena, it's possible for things to
>freeze when the air temperature is a few degrees above freezing. This
>only happens on clear, calm nights with lowish humidity, when the
>object can get colder than the air by black-body radiation.
Actually, you can get ice w/o exceptional radiational cooling
also, as anyone who's run industrial evaporative coolers w/ a burned
out sump heater can attest! (yeah, yeah, shoulda fixed it, I
know...) Evaporative coolers spray water from a sump down over a tube
bank w/ the working fluid inside, and big fans blow air up thru the
bank. Depending on the heat load, you can cool the working fluid
nearly to the ambient wet bulb temperature (dew point, approx.). The
problem arises if the dew point is below freezing but the dry bulb
above (and aren't paying attention!). If you don't keep the spray
water (these guys usually run in recirc w/ makeup) warm enough, the
droplets in the air stream will chill by evaporating partially to
below freezing (subcool) and freeze out as rime on the tube
bank/structure. Let this go very long, and the whole damn bank turns
to a block of ice, and ironically, your working fluid (AND your
compressors!) overheats. This could equate to windy, wet weather near
the freezing point with enough difference between dry and wet bulb
(i.e., less than approx. 100% humidity). I'd imagine planes could ice
up in a similar fashion.
--
Brad Whitehurst | Aerospace Research Lab
rb...@Virginia.EDU | We like it hot...and fast.
Brian Sheehan
>In article <4fo7cc$4...@opal.CyberGate.COM>, rikp...@CyberGate.COM (Richard Penny) says:
>>
>>: HappyBoy (paul...@borg.com) wrote:
>>
>>: : But if wind chill impacted inantimate objects in the same way, the
>>: : rain would freeze on your windshield. But it doesn't because the
>>: : actual temperature is above freezing. Wind Chill is, in effect, an
>>: : illusion.
>>
>>As I stated in a previous post, wind chill is neither a hoax nor an
>>illusion.
>So what is your point? What "happyboy" said is absolutely true.
So what is your point? What (Richard Penny) said is absolutely true.
a...@aber.ac.uk
|took a course on transport phenomena, it's possible for things to
|freeze when the air temperature is a few degrees above freezing. This
|only happens on clear, calm nights with lowish humidity, when the
|object can get colder than the air by black-body radiation.
|Fruit routinely is in danger of this, which is why citrus groves used
|to have smudge pots. The thick smoke prevented the loss of heat to
|space by reflecting the radiated energy back to the fruit. As I
|recall from the example problem we worked out, the air temperature can
|be as high as 36 deg F and the fruit will still freeze. (They stopped
|using smudge pots because they really polluted and now they use big
|fans.)
This is a problem for things with damp surfaces. The more energetic molecules
vapourise first, leaving the less energetic ones, cooling the surface to well
below ambient.. See my other post on this thread. Riding a motorbike at
just above zero in the sleet can leave you coated in ice :(
a...@aber.ac.uk
|>chill produces in TV meteorologists which are then repeated, like shock
|>waves through the populace ("it will be wind chills of 25 below tonight!!!
|> Brutally cold out there!!") when the TRUTH is that it is only 15 above
|>and, yeah, a little windy but it is USUALLY a little windy
|So, are you saying that the subjective feeling of (say) being in 15
|degree weather with a 20 mph wind *is not* similar in terms of felt
|coldness to being in -25 degree weather with no wind? Or are you saying
|that the physiological effects (frostbite, etc.) are not the same? Or
|are you saying that the scale is reasonably apt, but somehow is
|miscalibrated (and if so, what is your evidence for this)?
I have just had a chat with the Met Office, and unfortunately, the really
important figure in wet weather - that of forced evaporative cooling due to
the wind, - has simply nott been researched :(
You feel MUCH colder in a force 8 gale with rain at 5C than in a dry gale at
-5C
Joseph Scott Stuart
I think he's saying that the way it's usually reported is misleading.
The weather reports usually say something like, "It's 40 deg, but
with the wind chill it feels like 15 deg." When people hear that,
they probably think of the last time they were outside in 15 deg
weather, not the last time they were outside in 15 deg weather
_and_ no wind. So they get the wrong impression. Relative to
personal experience, it should be compared to a temperature
with moderate or typical winds and wind chill; that's what
people think when they hear, "it feels like x deg." But that's
not really a practical way to state the temperature or wind
chill. (What's a typical wind?)
I believe that most wind chill charts are already calibrated such that
"calm conditions" means about 2 or 3 mph winds.
Don't the Canadians usually use wind chill charts that show rate of
heat lost in watts/square meter? This would seem to clear up the
confusion that might result when you try to explain that it isn't
really -40, it only feels like it. On the other hand, in places where
people only occasionally have to worry about wind chill (like where I
grew up), most people would never gain enough experience with this
measure to understand what it means in practical terms. Having the
weather man say that it feels like -40 out seems like a good way to
convince people that they need to wear a hat. In that regard, I think
that it works fine. Anyone planning to spend a lot of time outside in
cold weather needs to have a better understanding of what is going on,
and recalibrating the wind chill charts will not help that.
scott
Bill Gascoyne
"Wind chill is a measurement of the rate of heat loss (of a human body?)
and not a measurement of temperature."
Correct or no? Comments?
---
Bill Gascoyne ----- Speak for them?
LSI Logic Corp. LSI |LOGIC| They hardly even
1501 McCarthy Blvd. | | listen to me!
MS E-197 -----
Milpitas, CA 95035 LSI addr: gascan@dcst16 internet: gas...@lsil.com
Brian Sheehan
>I am stunned this thread is still going, after months I think... but let
>me introduce this thought which has probably come up earlier.
> I see the Wind Chill Factor as a hoax because it bases itself on an
>assumption that we should use temperature with NO wind velocity as our
>starting conditions and then reduce that apparent temperature to account
>for the effects of wind. This would be fine if we usually experience
>conditions of zero wind velocity... but of course we don't. Thus, most
>times it is, say, 20 degrees outside there is also a wind of, say, 10
>mph... thus when we experience the real world conditions of 20 degrees the
>wind chill then is lower. The effect is "wind chill inflation", i.e.,
>making it seem much colder than it really is for dramatic effect on the
>weather reports on TV. When we grew up, 20 degrees wasn't that cold; now,
>when it is 20 degrees outside, the concommitant wind chill is usually, oh,
>-10 and my kids run around and talk about how bad it is outside and how
>it's too cold to take out the garbage, etc....
>MY SOLUTION IS to re-paramatize the wind chills to factor in an average
>wind speed we usually experience.
Excellent idea! All we need to do is replace those silly inexpensive mercury
thermometers and wind-chill charts with computerized systems that would
include not just temperature and windspeed detectors, but databases that would
enable us to determine the "average wind speed we usually experience" for any
given location. Come to think of it, the only practical way to do that would
be to include some sort of GPS feature in the device, along with the
historical records required. Of course, that would would make it just a tad
difficult to figure the wind chill if you were exploring an area where you
hadn't "experienced" an "average wind chill".
But seriously, kids, I think this message indicates the real reason that
individuals of a certain age have such a problem with the "wind chill factor".
It's just that they didn't have the WCF when they were young, so they can't
really compete with their kids any more when it comes to how bad it was in the
olden times. (It must be really awful in places where they've converted to the
metric system: grampa goes on and on about the 20 or 30 inches of snow that
used to fall almost daily when he was young- but little Courtney tells him "20
inches?!? we got 40 CENTIMETERS just last night!!!")
MC Hamster
>>So, are you saying that the subjective feeling of (say) being in 15
>>degree weather with a 20 mph wind *is not* similar in terms of felt
>>coldness to being in -25 degree weather with no wind? Or are you saying
>>that the physiological effects (frostbite, etc.) are not the same? Or
>>are you saying that the scale is reasonably apt, but somehow is
>>miscalibrated (and if so, what is your evidence for this)?
>I think he's saying that the way it's usually reported is misleading.
>The weather reports usually say something like, "It's 40 deg, but
>with the wind chill it feels like 15 deg." When people hear that,
>they probably think of the last time they were outside in 15 deg
>weather, not the last time they were outside in 15 deg weather
>_and_ no wind. So they get the wrong impression. Relative to
>personal experience, it should be compared to a temperature
>with moderate or typical winds and wind chill; that's what
>people think when they hear, "it feels like x deg." But that's
>not really a practical way to state the temperature or wind
>chill. (What's a typical wind?)
> Frank Crary
> CU Boulder
Yeah... what Frank Crary said. Brilliantly stated.
We are not talking practicality here... we are talking about simple truth,
honesty, and morality. It'd be a lot simpler to just have a flat income
tax, for all you anal types who like tidy, easy-to-use scales and
formulae, but society / government chooses not to because even though it
is a lot "messier", that it is RIGHT to have a graduated tax.
And I'm not CLOSE to being a grandpa yet... well, not THAT close... not
really that FAR either... hmmm... I wonder what my scale of measurement
should be...
Reinsborough
something, but in winter we try to avoid these places and head for woods
or "the east side of a house in a west wind" . I'm sure that the wind
chill factor is constantly changing for snowmobilers depending on the
speed they travel, yet one snowmobile suit serves all conditions. We
should dress for winter or summer appropertly and for the activity at
hand , and not get fooled or discouraged by this false reading called
"wind chill factor".......Ken
Richard G Clegg
: > But if wind chill impacted inantimate objects in the same way, the
: > rain would freeze on your windshield. But it doesn't because the
: > actual temperature is above freezing. Wind Chill is, in effect, an
: > illusion.
: Geez, and I thought that was because it's a lot warmer inside my car, what
: with me breathing in there and the desfroster on. And all this time I
: thought heating glass would keep things from freezing on it!
Umm... if it rains inside your car it's time to get a new car Ayse.
: ObPeeve: Basic Physics, and the numerous excuses that people seem to have
: for not getting enough of it in elementary school.
Indeed - had you understood Basic Physics you'd've sussed that
"Wind Chill" only affects things which are not in thermal equilibrium
with the environment and it causes them to cool faster. I.e. you cool
faster due to Wind Chill but the rain (being at the same temperature
as the wind) does not get any colder.
You can of course try to confirm your rival "heater" idea by turning
on and off the heater in your car and trying to get water to freeze at
a temperature above freezing point - I wish you luck.
ObPeeve: Basic Physics --- the numerous people who _think_ they understand
it.
--
Richard G. Clegg There ain't no getting round getting round
Dept. of Mathematics (Network Control group) Uni. of York.
email: ric...@manor.york.ac.uk
www: http://manor.york.ac.uk/top.html
Ayse Sercan
>
> But if wind chill impacted inantimate objects in the same way, the
> rain would freeze on your windshield. But it doesn't because the
> actual temperature is above freezing. Wind Chill is, in effect, an
> illusion.
Geez, and I thought that was because it's a lot warmer inside my car, what
with me breathing in there and the desfroster on. And all this time I
thought heating glass would keep things from freezing on it!
ObPeeve: Basic Physics, and the numerous excuses that people seem to have
for not getting enough of it in elementary school.
ObBackcountry: The stupidest thing I ever did while hiking in my misspent
youth was ignore the wind-chill factor and camp on the bare face of a
hill, rather than in the protection of the trees a couple miles further
on. I woke up in the morning frozen inside of my bag.
--
** ay...@netcom.com **
"We feel that in the years to come, the world is going to be a bigger
market for us than the U.S. It's just that there are more people, and
sooner or later, they're all going to have carpet." --John Balch
Claude Mathis
Sheehan) wrote:
-> mcha...@aol.com (MC Hamster) wrote:
->
-> >I am stunned this thread is still going, after months I think... but let
-> >me introduce this thought which has probably come up earlier.
->
-> > I see the Wind Chill Factor as a hoax because it bases itself on an
-> >assumption that we should use temperature with NO wind velocity as our
-> >starting conditions and then reduce that apparent temperature to account
-> >for the effects of wind. This would be fine if we usually experience
-> >conditions of zero wind velocity... but of course we don't.
Well, the fact is... the official temperatures ARE taken in a windless
situation. This is the only way to get accurate comparitive readings. So,
rather than being a "hoax", it makes perfect sence, unlike yourself.
Claude
/==========================/\=================================\
/ Claude Mathis //\\ Mathis Media \
/ ~~~~~~~~~~~~~ // \\ Internet Publishing \
\ cla...@mathis.com \\ // and Marketing /
\ get...@mathis.com \\// http://www.mathis.com/getinfo/ /
\==========================\/=================================/
Frank Crary
Richard G Clegg <ric...@manor.york.ac.uk> wrote:
> Indeed - had you understood Basic Physics you'd've sussed that
>"Wind Chill" only affects things which are not in thermal equilibrium
>with the environment and it causes them to cool faster. I.e. you cool
>faster due to Wind Chill but the rain (being at the same temperature
>as the wind) does not get any colder.
Actually, rain is probably a bad example. It's often out of
equilibrium with the environment. Freezing rain, for example,
is what you get when it's above freezing in the clouds but
below freezing at the surface. The rain falls too rapidly
for it to cool off and freeze, but once on the ground it
does freeze. Since it's out of equilibrium, wind speeds would
affect its cooling. (The same thing would apply, in reverse,
to snow falling on a warm surface; the stuff that melts
before it can accumulate.) A better example of what you
are describing might be a rock which has plenty of time
to come into equilibrium with its environment.
Frank Crary
CU Boulder
Edward Rice
rb...@rayleigh.mech.Virginia.EDU (Brad Whitehurst) wrote:
> Actually, you can get ice w/o exceptional radiational cooling
> also, as anyone who's run industrial evaporative coolers w/ a burned
> out sump heater can attest! (yeah, yeah, shoulda fixed it, I
> know...) Evaporative coolers spray water from a sump down over a tube
> bank w/ the working fluid inside, and big fans blow air up thru the
> bank. Depending on the heat load, you can cool the working fluid
> nearly to the ambient wet bulb temperature (dew point, approx.). The
> problem arises if the dew point is below freezing but the dry bulb
> above (and aren't paying attention!). If you don't keep the spray
> water (these guys usually run in recirc w/ makeup) warm enough, the
> droplets in the air stream will chill by evaporating partially to
> below freezing (subcool) and freeze out as rime on the tube
> bank/structure. Let this go very long, and the whole damn bank turns
> to a block of ice, and ironically, your working fluid (AND your
> compressors!) overheats. This could equate to windy, wet weather near
> the freezing point with enough difference between dry and wet bulb
> (i.e., less than approx. 100% humidity). I'd imagine planes could ice
> up in a similar fashion.
I don't recall being warned much about air pressure differences on the
wings producing external icing, but it's theoretically possible. High
airspeeds may keep it from happening, someone would have to examine the
microphysics of the situation -- perhaps at a speed sufficient to produce
the effect, the ice can be guaranteed to sublimate away at least as fast as
it builds up, so only a trivial amount can ever be produced. (That's just
a SWAG.)
For non-fuel-injected piston aircraft, of course, the danger of icing
within the carburetor is an obvious and /extremely/ real one -- most pilots
experience it, unlike almost everything else we are trained to deal with.
Frank Crary
Chris Sibley <ctsibley@princeton> wrote:
> Yes. Exactly. The wind chill tables take the rate of heat loss from a
>98.6 F body at a given ambient temperature and adds that to the rate of
>heat loss due to convective cooling of a 98.6 F body at a given wind
>speed. The "temperature with wind chill" just tells you the ambient
>temperature at which (without wind) the rate of heat loss from your body
>would be the same as it is at the actual temperature with wind.
> Important consequence: Unless you're talking about an object at or
>near human body temperature, wind chill doesn't apply. This tells you how
>fast we get cold, not how fast our equipment gets cold.
Unfortunately, that's not quite correct. Wind chill is, as you
said, a measure of how rapidly an object at 98.6 F will
loose heat. For an object at a different temperature, wind
chill still applies (i.e. it's still loosing extra heat
due to forced convection) but the calculated "temperature
with wind chill" would be different from what is traditionally
reported. The real problem, as I see it, is that the
important temperature is the external, surface temperature
of the object; the temperature of whatever is exposed to
the outside air and wind. So, strictly speaking, wind
chill calculated for a 98.6 F temperature tells you
how quickly a healthy, nude person would loose heat
(and even then, it's not quite accurate, since
skin temperature is usually several degrees cooler
that the core temperature of 98.6 F.) If you are
wearing a coat, what matters is the temperature of
the outside of the coat, which is _not_ 98.6 F.
So the usual "temperature with wind chill" doesn't
really tell you how quickly a person would loose
heat. I suspect these details wouldn't change the
exact number by more than a few degrees, so the
usually stated wind chill is a good approximation.
But it is only an approximation.
Frank Crary
CU Boulder
Phillip J. Birmingham
>Richard G Clegg <ric...@manor.york.ac.uk> wrote:
>> Indeed - had you understood Basic Physics you'd've sussed that
>>"Wind Chill" only affects things which are not in thermal equilibrium
>>with the environment and it causes them to cool faster. I.e. you cool
>>faster due to Wind Chill but the rain (being at the same temperature
>>as the wind) does not get any colder.
>
>Actually, rain is probably a bad example. It's often out of
>equilibrium with the environment. Freezing rain, for example,
Jayzus H. Christ, why am I getting into this thread?
Heat transfer to the air is a lot faster when it's windy than not.
If you go outside, you'll lose more heat in a stiff breeze than in still
air; the wind chill index basically tells you what temperature still air
would have to be to bring about a similar rate of heat loss.
If you stand outside until your mitochondria say "fuck this for a
lark," your corpse will cool down faster in a stiff breeze than in still
air. At the end, however, it will reach the same temperature in both
cases -- that of the ambient air.
Wind chill is a perfectly valid concept that is abused by weenies
who think that fifteen Fahrenheit is not a sufficiently impressive degree
(heh) of coldness.
--
Phillip J. Birmingham
phi...@mcs.com "Tampering in God's Domain since 1965!" TMA#7
http://www.mcs.com/~phillip/home.html
Richard Penny
: Apparently the people who believe that this is all a hoax perpetrated
: by weathermen who have never left the city also wouldn't believe that
: sitting in front of a fan cools you off on a hot summer day. It's all the
: same thing.
Not necessarily. The effect of a fan on a hot day is primarily to increase
evaporative cooling. Convective cooling requires conductive cooling as a
prerequisate, and if the ambient temperature is greater than the skin
temperature, then heat does not conduct in the direction of body to air.
Here is what Guyton and Hall have to say on pp. 912 to 913,
"Conduction. As shown in Fig. 73-4, only minute quantities of heat
are normally lost from the body by direct conduction from the surface of
the body to other objects, such as a chair or a bed. On the other hand,
loss of heat by _conduction to air_ does represent a sizable proportion of
the body's heat loss (about 15%) even under normal conditions. It will be
recalled that heat is actually the kinetic energy of molecular motion, and
the molecules of the skin are constantly undergoing vibratory motion. Much
of the energy of this motion can be transferred to the air if the air is
colder than the skin, thus increasing the velocity of motion of air
molecules. Once the temperature of the air immediately adjacent to the
skin equals the temperature of the skin, no further loss of heat occurs
because now an equal amount of heat is conducted from the air to the body.
Therefore, conduction of heat from the body to the air is self-limited
_unless the heated air moves away from the skin_, so that new unheated air
is continually brought in contact witht he skin, a process called air
convection.
Convection. The removal of heat from the body by convection air
currents is commonly called heat loss by convection. Actually, the heat
must first be _conducted_ to the air and then carried away by convection
currents.
A small amount of convection almost always occurs around the body
because of the tendency for the air adjacent to the skin to rise as it
becomes heated. Therefore, a nude person seated in a comfortable room
without gross air movement still loses about 15% of his or her heat by
conduction to the air and then by air convection away from the body."
--
The wind chill tables do not take evaporative cooling into account.
Brad Whitehurst
Edward Rice <ehr...@his.com> wrote:
>In article <DMryK...@murdoch.acc.Virginia.EDU>,
>rb...@rayleigh.mech.Virginia.EDU (Brad Whitehurst) wrote:
>
> > Actually, you can get ice w/o exceptional radiational cooling
> > (i.e., less than approx. 100% humidity). I'd imagine planes could ice
> > up in a similar fashion.
>
>I don't recall being warned much about air pressure differences on the
>wings producing external icing, but it's theoretically possible. High
>airspeeds may keep it from happening, someone would have to examine the
>microphysics of the situation -- perhaps at a speed sufficient to produce
>the effect, the ice can be guaranteed to sublimate away at least as fast as
>it builds up, so only a trivial amount can ever be produced. (That's just
>a SWAG.)
It may not be a big problem, but it could happen to any
surface moving through the air (or having air move over it), not just
a wing, since it is not really pressure dependent (well, within
limits). Get the surface wet, then blow cold air (a little above
freezing) that is less than saturated over the surface. Some of the
water on the surface will evaporate, cooling the surface. In the
limit, you will approach the wet bulb temperature of the air, which
can be below freezing. If that happens, ice will start to form. Such
weather is not uncommon in the Mid Atlantic, where we get rain
slightly above freezing, but the actual humidity is not 100%.
Drive your car around on the highway for a while, and you can
watch ice forming on parts which aren't well heated from the inside,
like antennas, racks, grilles, even though a thermometer sitting at the
side of the road reads above freezing. For example, at 36 deg F and
50% relative humidity (sea level), the wet bulb temperature is about
30 deg F, so if you take a thermometer and wrap a wet sock around it
and wave it about briskly in 36F, 50% weather, it will actually read
30F, and will get crusty w/ ice. This discussion assumes negligible
heat generation so heat transfer in the steady state will go to zero.
In the case of steady internal heat generation, such as a
glass of water w/ a thermostatic aquarium heater in it, you may or may
not get the surface of the glass below freezing, depending on the
strength of the heater. What you will see is a lower surface
temperature of the glass once you start blowing air over it due to the
increased convection coefficient (even if the middle of the water in
the glass stays the same temperature from the heater), therefore a
steeper temperature gradient through the wall of the glass. Actually,
this is true to some extent whether the outside of the glass is wet or
not. As a reference, when computing insulation ratings for walls of
buildings, one commonly assigns an average "resistance" to the inside
(still air) and outside (15 mph wind) surfaces. The outside surface
(per ASHRAE) is about 3.5 less resistance than the inside.
BTW, just found a technical description of the wind chill
index (an older book...may have moved a bit): "It is determined
empirically by an equation which is used to describe the rate of heat
loss from a litre cylinder of water at 33C (91.4F) as a function of
ambient temperature and wind velocity." (Marks 8th edition) It goes
on to give the WCI formulas:
WCI= (10.45 - V + 10*sqrt(V))*(33-ta) kcal/m^2/hr
where V= wind speed in m/sec and ta= ambient temp in deg C
The "equivalent wind chill temperature" is expressed as
teq = -0.04544(WCI) + 33degC
So the WCI ignores (apparently) humidity, focussing only on
the effect of wind on increasing heat transfer. This means that, yes,
WCI can't be "measured" by a simple thermometer, since (w/o heat
generation) a thermometer has no temperature gradient from its
interior to the air when in equilibrium, so the whole device is (at
equilibrium) at the "dry bulb" temperature. Objects w/ internal
generation of heat (people, my glass w/ heater) do sustain a steady
state temperature gradient from inside to out. The actual surface
temperature is _above_ the air's dry bulb temp.(in a cooling
situation), and if the internal temperature is constant, that surface
will fall in temperature as the wind increases. The higher air
velocity causes an increase in the convection heat transfer
coefficient, thus an increase in the temperature gradient at the
surface.
*Whew* That's enough geeking out for one cup of coffee! ;-)
Douglas Murray
Penny) writes:
> The wind chill tables do not take evaporative cooling into
account.
>
articles on the development of the wind chill index (Siple, P.A.,
"Measurements of drey atmospheric cooling in subfreezing temperatures",
Amer. Philosophical Soc., Vol. 89, No. 1, Apr 1945), which summarizes
even early work and (Falconer, R.A., "Windchill, a useful wintertime
weather variable", Weatherwise, December 1986) which summarizes Siple's
work in a more readible manner, you can get a description of the
techniques applied to determine windchill.
Early work (Hill, 1919 the"wet kata thermometer"; Stone 1939, Eaton
1940) relied on either wind speed and dry temperature or windspeed and
wet bulb temperature (which did include evaporation). Siple (a Major
in the U.S. Army, a geographer and Leader of the West Base U.S.
Antarctic Service) recognized that the factors included in the kata
thermometer experiments overestimated actual wind cooling effects.
Siple noted that "the principal factors which make the human body the
most perplexing of the variables are: the increase in metabolism or
heat output of the body with activity, the amount of blood ciculating
in the skin affecting conduction and radiation of heat from it,
perspiration controlling the rate of evaporation, storage of heat in
the tissues, emotion, fatigue, clothing and numerous minor factors..."
Thus he saw people as an important variable in wind chill. He did two
series of experiments:
1)he put water in exposed containers on a tower on the ice sheet and
timed the rate of freezing as a function of temperature and wind speed
(some evaporation included)
2) using "volunteers" standing out on the ice sheet he established "the
length of elapsed time before exposed portions of the body turned white
or actually froze at various wind velocities and subfreezing
temperatures. Subjects were unclothed and in the shade for these
tests." Core body temperatures for the volunteers were measured using
rectal thermometers (not that they were probably interested in sitting
anyway).
Data from these two sets of experiments were combined to derive the
wind chill index. Clearly evaporation was included in the original
data. As Siple noted, however, many variables affect the rate of
cooling beyond simple wind speed and temperature, including individual
physiological condition.
Doug M
Richard Penny
: 1)he put water in exposed containers on a tower on the ice sheet and
: timed the rate of freezing as a function of temperature and wind speed
: (some evaporation included)
I stand corrected.
robert hagg
I missed the begining of this. Please forward to me. I would like the reference,journel
etc the report you mentioned came from.
I've seen this topic a number of times now and grin when i see hoax hoax.
I know from first hand experience that when I sit in a tent at -20F without a hat my ears don't get
frostbite. Once i step out of the tent into 20 knot windsd, -20F my ears will get gray in very short
order. I can also say from recent first hand experience that the pipes in our apartment froze and
burst where there was a direct draft and didn't where there wasn't. Before the flamers start the
heater went out and the water was not moving in the pipes.
The plumber, old guy doing it for 30 years, practical experience no advanced degree in physics using
first hand experience, looked at me like i was dumb and said, The pipes always freeze where there's a draft.
(The temperature was the same throughout the apartment, and pipes in the outside wall didn't freeze just the
on along the entry way)
As one that does science i asked, So the wind actually causes the water to freeze in the pipes faster? He looked
at me smiled and went about his buisness as if to say, its common knowledge don't you beleive your eyes dummy
Some here are working on a polar library. I've been attempting to get one started myself for some time.
For my own answer to what i thought was an obivious question, I'll attempt to find a few papers on it
and attempt some experiemnts myself. Its about 18degF right now.
PS. What part of the country are you guys from?
--
Rob Hagg, Lamont-Doherty Earth Observatory Route 9W, Palisades, N.Y. 10964
rh...@ldeo.columbia.edu Voice: (914) 365-8744 Fax: (914) 359-6940
You can measure a person by the opposition it takes to discourage them.
--Robert C. Savage
Charles R. Tenney
Frank Crary <fcr...@rintintin.Colorado.EDU> wrote:
>Actually, rain is probably a bad example. It's often out of
>equilibrium with the environment. Freezing rain, for example,
>is what you get when it's above freezing in the clouds but
>below freezing at the surface. The rain falls too rapidly
>for it to cool off and freeze, but once on the ground it
>does freeze. Since it's out of equilibrium, wind speeds would
>affect its cooling.
Argh. The rest of this is fine, but wind speeds wouldn't do anything
(although massive and numerous wind shears might). The picture comes up
of raindrops falling down with the wind whipping around them, cooling them
off--which of course doesn't happen. The raindrop, upon entering a wind
layer, will quickly be accelerated to the speed of the wind, at which
point the only relative motion between raindrop and air is vertical. The
wind does not blow on the raindrops, it carries them. Only when the drop
falls into a layer with different wind velocity than that of the layer
above will it be blown upon, and then only briefly. (Hence the wind shear
comment.) People often have a similar problem visualizing the effect of
wind on airplanes, thinking that a cross wind blows the plane to the side
(i.e., exerts some force bodily on the side of the fuselage, over the
course of hundreds of miles) when the truth is, the plane is carried
sideways in a river of air that happens to be moving relative to the
earth.
This, of course, is why rain falling in windy conditions appears to fall
on a slant. Appears to, because it does.
ObPreEmptive Explanation: Please, don't even think about saying "the rain
will have more time to cool if it's being carried by the wind, since it
has further to go."
--
--
Charles R. Tenney charles...@unc.edu | What would the UNC school of
| Medicine want with my opinions?
"My karma ran over my dogma." | What would I want with theirs?
Jim Shaw
> first hand experience, looked at me like i was dumb and said, The pipes
always freeze where there's a draft.
The water didn't freeze from wind chill unless the pipe was wet and
evaporation caused the heat loss. What really happened is that the wind
brought a constant supply of cold air to bear on the pipe, rather than
having still air which insulates.
DouglasShaw
>mcha...@aol.com (MC Hamster) wrote:
>
>>I am stunned this thread is still going, after months I think... but let
>
Go stand, naked, in a walk in freezer for one hour. After you have done
that, then tell me what zero wind velocity feels like.
Brian Sheehan
Golly, Doug, thanks for giving me credit, but "bshe...@world.std.com (Brian
Sheehan)" wrote no such thing. Perhaps your cutting and pasting skills need a
brushup.
Now then, if you'll excuse me, once I get my socks off, I'll be stepping into
my freezer.
Geoff Miller
In article <4gjdbv$1d...@bigblue.oit.unc.edu> ten...@med.unc.edu
(Charles R. Tenney) writes:
> ObPreEmptive Explanation: Please, don't even think about saying "the rain
> will have more time to cool if it's being carried by the wind, since it
> has further to go."
Well, why the hell not? That certainly makes abundant sense to me.
After all, the longer something is exposed to a stimulus, the greater
the effect of that stimulus on it will be, right? Hey, *you* opened
this Pandora's box...
ObPeeve/WindShear: Having my flight out of DFW to San Jose delayed
when that Delta L-1011 went in back in '85.
Geoff
--
"Commit senseless acts of violence and random brutality"
Charles R. Tenney
Geoff Miller <geo...@netcom.com> wrote:
>
>
>In article <4gjdbv$1d...@bigblue.oit.unc.edu> ten...@med.unc.edu
>(Charles R. Tenney) writes:
>
>> ObPreEmptive Explanation: Please, don't even think about saying "the rain
>> will have more time to cool if it's being carried by the wind, since it
>> has further to go."
>
>Well, why the hell not? That certainly makes abundant sense to me.
>After all, the longer something is exposed to a stimulus, the greater
>the effect of that stimulus on it will be, right? Hey, *you* opened
>this Pandora's box...
Only because the longer path doesn't translate to a longer flight time:
the extra path length is due to horizontal motion (as seen from the
ground; as seen from the raindrop, there is no horizontal motion relative
to the air except just after a wind shear). The vertical path length is
the same, and that's travelled at terminal velocity for nearly all of the
raindrop's flight time. Thus, horizontal motion doesn't affect the flight
time. In freshman physics classes, this concept is traditionally
explained in terms of a hunter aiming a rifle barrel straight at a monkey
(must set the range on the sights to zero, I guess) and firing just as the
monkey drops from the tree. Although the monkey has no horizontal velocity
and the bullet does, they fall at the same rate, resulting in a plugged
monkey.
This, of course, presumes no up- or down-drafts (often a wildly
inaccurate presumtion, especially in a thunderstorm), and that the
rain-producing layer in the cloud is all at one level. (For extra credit,
the student may figure out why changes in the ground height do NOT affect
the result. Hint: the damp observer is assumed to stay in one place
while the wind shifts.)
Peeve: At Amherst College, the hunter-cum-monkey gedanken experiment was
demonstrated with a little stuffed dog and a rather large dart. The dart
was fired horizontally at the doggie just as the doggie dropped, with dog
and dart starting at the ceiling on opposited sides of a large lecture
hall. Naturally, the doggie was impaled every time. Since I took the
one-semester think-you're-a-hotshot version of freshman physics, I never
got to see this demo. Eventually, that stuffed dog, which had already spent
all of its useful life in free-fall, went into space on a shuttle mission,
courtesy of an Amherst grad who was an astronaut.
M Holmes
: Peeve: At Amherst College, the hunter-cum-monkey gedanken experiment was
: demonstrated with a little stuffed dog and a rather large dart. The dart
: was fired horizontally at the doggie just as the doggie dropped, with dog
: and dart starting at the ceiling on opposited sides of a large lecture
: hall. Naturally, the doggie was impaled every time. Since I took the
: one-semester think-you're-a-hotshot version of freshman physics, I never
: got to see this demo. Eventually, that stuffed dog, which had already spent
: all of its useful life in free-fall, went into space on a shuttle mission,
: courtesy of an Amherst grad who was an astronaut.
Peeve: I was expecting to hear that the doggie got plugged by a meteor.
Endings are never as good as you expect.
: Charles R. Tenney
FoFP
--
"You've certainly convinced me that things are not merely loony at
Smith; the inmates are running the asylum, and charging $26,320 a
year to share the experience."
-- Howard.E.Motteler