Global warming due to asphalt?
Steve
concrete surfaces make to global warming?
I visited relatives that live on the other side of a hill from the "city"
and it is about 10 degrees cooler there. I frequently hear weather reports
that speak of temperatures being higher in cities.
Given the prevalence of pavement as a good thermal mass, I have to wonder if
it isn't a significant contributor to climate change.
If pavement is a significant contributor, there are many things we could do.
Planting trees along freeways to shade the pavement. Covering buildings
with vines to reduce the absorbtion, etc.
Regards,
Steve
Jeff
> Has anyone done the calculation of the contribution that asphalt and
> concrete surfaces make to global warming?
Look up Urban Heat Island.
I live in one (Atlanta).
There's a slight temperature rise over surrounding areas, but it is not
that much. What we do get this time of year is popup thunderstorms as
the island cools in the evening.
http://en.wikipedia.org/wiki/Urban_heat_island
It's a complicated effect and is more tilted towards large urban areas
generating their own weather rather than any warming trend. The net
global warming effect is negligible.
A larger problem in many places is that the hardened surfaces lead to
faster runoff. This is particularly true of concrete, but also true in
farmland areas where border woodsy/swampy areas have been cultivated...
Jeff
PhattyMo
No to mention the heat from all the human bodies,and appliances.
There are more heat sources in a city.
You
"Steve" <nospam_...@comcast.net> wrote:
> I frequently hear weather reports
> that speak of temperatures being higher in cities.
Temps are ALWAYS higher in a city, because that is where ALL that power
is dissipated. Duh......
Steve
news:you-4152A4.1...@netnews.worldnet.att.net...
Hmmm...
On a clear sunny day about 1 KW/M^2 (kilowatt per square meter) reaches the
surface of the earth. That's about 2.6 megawatts per square mile.
I know that if that energy falls on concreate or asphalt (a good thermal
mass) the heat is stored and re-released at night. If it falls on foliage
it tends to get converted into chlorphyll.
It is certainly not obvious to me that this is a small effect. Especially
when you consider how much of the earths surface we have covered with
concrete and asphalt. Just bring up google earth and zoom in just about
anywhere in the US and you will find a lot of thermal mass.
Regards,
Steve
David Williams
-> On a clear sunny day about 1 KW/M^2 (kilowatt per square meter)
reaches the
-> surface of the earth. That's about 2.6 megawatts per square mile.
->
-> Regards,
-> Steve
Ummm... There are about 1600 metres in a mile, so 1600 x 1600 or 2,560,000
square metres in a square mile. So there are about 2.6 GIGAwatts of solar
energy falling on each square mile of ther earth愀 surface.
dow
You
"Steve" <nospam_...@comcast.net> wrote:
but you seem to be ignoring the FACT that the suns energy is only PART
of the Total Energy being dissipated in any one area. Think of ALL the
electrical energy we pump into cities. Thousands of Megawatts. Where
does all that energy go? It goes up in HEAT, in the cities where it is
USED. That heats the AIR in those cities, and that causes a Temp Rise
in cities that isn't there in rural areas. How much energy does a tree
dissipate, or grass, or small animals, compared to the amount of
electrical energy dissipated, per square mile, in a city? Duh......
J. Clarke
Google "heat island".
--
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)
Steve
news:1216033763.9...@bayman.org...
I stand corrected. Those nasty decimal places anyhow.
A few interesting statistics from:
http://www.solcomhouse.com/solarpower.htm
---
All the energy stored in Earth's reserves of coal, oil, and natural gas is
matched by the energy from just 20 days of sunshine.
In 40 minutes of daylight The SUN releases upon The Earth the amount of
energy that is consumed by the entire population of the planet in ONE YEAR.
Each day more solar energy falls to the Earth than the total amount of
energy the planet's 6 billion inhabitants would consume in 27 years.
---
If these statistics are true, I would not be a bit surprised if the "Heat
Island" effect is more significant than the greenhouse effect. Of course
they are not independent, and the global effect of either are extremely hard
to measure with any certainty.
Regards,
Steve
David Williams
-> of the Total Energy being dissipated in any one area. Think of ALL the
-> electrical energy we pump into cities. Thousands of Megawatts. Where
-> does all that energy go? It goes up in HEAT, in the cities where it is
-> USED. That heats the AIR in those cities, and that causes a Temp Rise
-> in cities that isn't there in rural areas. How much energy does a tree
-> dissipate, or grass, or small animals, compared to the amount of
-> electrical energy dissipated, per square mile, in a city? Duh......
When the sun is shining on the earth's surface, about one GIGAwatt of
heat per square kilometre is produced by it. It's true that large
cities consume several gigawatts of electrical power, but they have
areas of many square kilometres. So the amount of heat, per square
kilometre, that the electrical power produces is much less than the
amount from sunshine.
The reason why asphalt gets a lot hotter than grass when the sun shines
on it is mainly because water evaporates from the grass and not from
the asphalt. Very dry grass does get hot, but fresh green grass does
not. The same is true of other vegetation.
dow
Bob F
Another question would be - how much energy is re-radiated back into space at
night from the hot pavement. It may even reduce the warming effect compared to
greenery.
David Williams
-> > on it is mainly because water evaporates from the grass and not from
-> > the asphalt. Very dry grass does get hot, but fresh green grass does
-> > not. The same is true of other vegetation.
-> >
-> Another question would be - how much energy is re-radiated back into space a
-> night from the hot pavement. It may even reduce the warming effect compared
-> greenery.
I don't think the equilibrium temperatures of asphalt and grass would
be very different at night, unless a significant amount of moisture is
still evaporating from the grass, in which case it would be *cooler*
than the asphalt.
dow
T. Keating
<nospam_...@comcast.net> wrote:
>"You" <y...@shadow.orgs> wrote in message
>news:you-4152A4.1...@netnews.worldnet.att.net...
>> In article <gIKdnbEGUPZK2-zV...@comcast.com>,
>> "Steve" <nospam_...@comcast.net> wrote:
>>
>>> I frequently hear weather reports
>>> that speak of temperatures being higher in cities.
>>
>> Temps are ALWAYS higher in a city, because that is where ALL that power
>> is dissipated. Duh......
>
>Hmmm...
>
>On a clear sunny day about 1 KW/M^2 (kilowatt per square meter) reaches the
>surface of the earth. That's about 2.6 megawatts per square mile.
Exponent error... that would be 2.6 gigawatts per square mile.
daestrom
Well now you've opened a 'can of worms'. The grass is cooler because a tiny
bit of energy is stored in plant material and most is used to evaporate
water. But how the energy of that water gets released is complex. Often it
is given back to the upper atmosphere when forming clouds and rain. And
that air, being cooler than the air near the planet surface gives its heat
back to space. But water in the atmosphere is a 'greenhouse gas' in that it
absorbs infra-red radiation from below. My head hurts thinking about just
some of the factors that are involved.
daestrom
RF
With concreted or asphalted areas there should be
a certain minimum coverage with trees to provide
shade, reduce the overall heating effect, and make
it a more comfortable place to be.
RicodJour
>
> The reason why asphalt gets a lot hotter than grass when the sun shines
> on it is mainly because water evaporates from the grass and not from
> the asphalt. Very dry grass does get hot, but fresh green grass does
> not. The same is true of other vegetation.
You make it sound like the mass and color of the object/surface have
nothing to do with absorption of solar energy.
R
fusion
highways even without traffic,the temperature goes up a lot,it's the
asphalt acting as a heater...we can install thermal tubes and PV on
the sides of the highways,on top, with turbines if possible and
concentrators,etc.,the same for parking lots,we can cover them with
solar panels,etc., but first we got to save our assets,read below if
you want to...
http://constantchange-fusion.blogspot.com/
David Williams
-> >
-> > The reason why asphalt gets a lot hotter than grass when the sun shines
-> > on it is mainly because water evaporates from the grass and not from
-> > the asphalt. Very dry grass does get hot, but fresh green grass does
-> > not. The same is true of other vegetation.
-> You make it sound like the mass and color of the object/surface have
-> nothing to do with absorption of solar energy.
-> R
The mass has nothing to do with it. The colour does affect the amount
of light that is absorbed, but it also affects the amount that is
emitted. The equilibrium temperature of any body an a given radiation
environment is independent of the colour.
This is easy to prove. Imagine two bodies, of different colours, in a
box with walls that are perfect reflectors of light. If one body came
to equilibrium at a different temperature than the other, it would be
possible to set up a heat engine between them so you'd have a perpetual
motion machine. This can't happen, so the equilibrium temperatures of
the two bodies must be equal.
dow
J. Clarke
With the conditions you gave both bodies will be at absolute zero and
will remain there. Does one of them have an initial temperature?
David Williams
-> > a
-> > box with walls that are perfect reflectors of light. If one body
-> > came
-> > to equilibrium at a different temperature than the other, it would
-> > be
-> > possible to set up a heat engine between them so you'd have a
-> > perpetual motion machine. This can't happen, so the equilibrium
-> > temperatures of
-> > the two bodies must be equal.
-> With the conditions you gave both bodies will be at absolute zero and
-> will remain there. Does one of them have an initial temperature?
-> --
-> --
-> --John
I didn't specify they were at absolute zero. Their initial temperatures
don't matter. They will equilibrate to *equal* temperatures. That's the
point.
dow
J. Clarke
Show us the calculation.
RicodJour
> -> On Jul 16, 10:54 pm, david.willi...@bayman.org (David Williams) wrote:
Ah. I apologize for my earlier admonition to quote correctly. You
apparently can only see your own name. Don't think of it as a
failing, think of it as "It's all about me." That works for most
people.
> -> > The reason why asphalt gets a lot hotter than grass when the sun shines
> -> > on it is mainly because water evaporates from the grass and not from
> -> > the asphalt. Very dry grass does get hot, but fresh green grass does
> -> > not. The same is true of other vegetation.
>
> -> You make it sound like the mass and color of the object/surface have
> -> nothing to do with absorption of solar energy.
>
> The mass has nothing to do with it. The colour does affect the amount
> of light that is absorbed, but it also affects the amount that is
> emitted. The equilibrium temperature of any body an a given radiation
> environment is independent of the colour.
>
> This is easy to prove. Imagine two bodies, of different colours, in a
> box with walls that are perfect reflectors of light. If one body came
> to equilibrium at a different temperature than the other, it would be
> possible to set up a heat engine between them so you'd have a perpetual
> motion machine. This can't happen, so the equilibrium temperatures of
> the two bodies must be equal.
Last I checked the world isn't a perfectly reflective box. We're also
talking about a system that is open on the local level, not closed,
and there are other factors at work.
How you can say that mass has nothing to do with heat transfer? A
grassy surface is analogous to fiberglass insulation where the grass
"layer" contains air pockets which effectively slow down heat
transfer. You can model that anyway you want, but the net effect is
reduced heat transfer.
You wrote: "The reason why asphalt gets a lot hotter than grass when
the sun shines on it is mainly because water evaporates from the grass
and not from
the asphalt. Very dry grass does get hot, but fresh green grass does
not."
That is simply wrong. Your did not mention color at all which is
obviously the main factor. Artificial turf is grass colored and does
not benefit from respiration cooling, yet the surface temperature is
relatively close to real grass.
Strive for consistency.
R
David Williams
-> grassy surface is analogous to fiberglass insulation where the grass
-> "layer" contains air pockets which effectively slow down heat
-> transfer. You can model that anyway you want, but the net effect is
-> reduced heat transfer.
-> You wrote: "The reason why asphalt gets a lot hotter than grass when
-> the sun shines on it is mainly because water evaporates from the grass
-> and not from
-> not."
-> obviously the main factor. Artificial turf is grass colored and does
-> not benefit from respiration cooling, yet the surface temperature is
-> relatively close to real grass.
-> Strive for consistency.
-> R
I didn't say that asphalt and dry grass will *rapidly* reach the same
equilibrium temperature. Certainly, the process will be slower in the
case of the grass.
I don't believe that artificial turf is cool. In full sunshine, it must
get quite hot. However, if you step on it with a bare foot, your skin
will be heated quite slowly compared with stepping on hot asphalt since
the heat conductivity of the turf is lower, so it won't feel as hot.
dow
David Williams
-> > temperatures don't matter. They will equilibrate to *equal*
-> > temperatures. That's the point.
-> Show us the calculation.
-> --
-> --
-> --John
temperatures, a heat engine can remove energy fromn them, converting
the heat they contain to some other form of energy. That's a violation
of the Second Law of Thermodynamics, which says that systems tend
toward the state of highest entropy, in which other forms of energy
have become heat. So either the Second Law is wrong or the bodies in
the box will come to equal temperatures. You choose which to believe...
dow
J. Clarke
> -> > I didn't specify they were at absolute zero. Their initial
> -> > temperatures don't matter. They will equilibrate to *equal*
> -> > temperatures. That's the point.
>
> -> Show us the calculation.
>
> -> --
> -> --
> -> --John
>
> No calculation is needed. If the two bodies equilibrate to unequal
> temperatures, a heat engine can remove energy fromn them,
Uh, tell us how to make this heat engine that works without
transferring any energy from one reservoir to the other.
Two isolated bodies of different colors in a perfectly reflective
cavity is a different case from two bodied of different colors
connected by a heat engine in a reflective cavity. You are taking the
second case and claiming that it proves something about the first.
> converting
> the heat they contain to some other form of energy. That's a
> violation
> of the Second Law of Thermodynamics, which says that systems tend
> toward the state of highest entropy, in which other forms of energy
> have become heat. So either the Second Law is wrong or the bodies in
> the box will come to equal temperatures. You choose which to
> believe...
What I'm seeing is arm waving, not a calculation.
J. Clarke
Try this experiment--take two pieces of oriented strand board, paint
one white and the other black. Put each on the beach in Miami around
noon on a clear day and let it sit for an hour or however long you
think it takes for them to reach "equilibrium". At the end of this
time do some pushups with one hand on each and let us know how you
make out.
Steve
You are oversimplifying based on ideal steady-state conditions.
A greater thermal mass will take longer to warm up, and thus stay cooler
longer.
The rate of heat transfer is proportional to the difference in temperatures
(IIRC it's one of Newton's laws).
So, as the greater thermal mass increases in temperature gradually, it's
loss to the surrounding air will be less than if it were heated
instantaneously. Over time the greater thermal mass will lose less heat to
its surroundings as it is absorbing more energy. It isn't really gaining
more, but has a similar result.
One way to think of the earth is as a spinning sphere. Energy falls on one
face of the sphere and is radiated from the other. Certainly the amount of
energy retained by the sphere can be changed by modifying the characterstics
of the surface. Just like the sphere the earth loses energy to its
surroundings. It is not a closed system.
Regards,
Steve
David Williams
-> one white and the other black. Put each on the beach in Miami around
-> noon on a clear day and let it sit for an hour or however long you
-> think it takes for them to reach "equilibrium". At the end of this
-> time do some pushups with one hand on each and let us know how you
-> make out.
-> --
-> --John
When the weather hereabouts improves (we've already had more rain than
has fallen in June and July in any previous year since records began,
and sunshine is very rare), I'll do something along those lines. I'll
probably use a thermometer, and I'll try to minimize convective cooling
of the surfaces by by air. I do not expect to find that the
temperatures are very different.
Maybe you should try it too.
dow
David Williams
-> > temperatures, a heat engine can remove energy fromn them,
-> Uh, tell us how to make this heat engine that works without
-> transferring any energy from one reservoir to the other.
Exactly. Any heat engine takes heat from a warmer reservoir and dumps
some of it to a cooler one. If the reservoirs are at equal
temperatures, it won't work.
-> Two isolated bodies of different colors in a perfectly reflective
-> cavity is a different case from two bodied of different colors
-> connected by a heat engine in a reflective cavity. You are taking the
-> second case and claiming that it proves something about the first.
They are different only if the heat engine is working and transferring
heat. If the bodies are at equal temperatures, the engine can't
transfer any heat, so its presence is irrelevant.
-> What I'm seeing is arm waving, not a calculation.
What kind of calculation do you want?
This is all standard physics. Look in any textbook.
Or ask a potter. When pots are being fired in a kiln, they can be seen
by looking through a small hole in its door. When they are all at a
uniform high temperature, red hot, they become virtually impossible to
see, despite the fact that they may have been coated in glazes of very
different colours. Compared with the dark-coloured ones, the
light-coloured ones emit less light but reflect more, so the total
brightnesses of the surfaces are equal. Equal temperatures correspond
to equal radiation environments, regardless of colour.
As I said. Standard physics.
dow
David Williams
-> longer.
-> The rate of heat transfer is proportional to the difference in temperatures
-> (IIRC it's one of Newton's laws).
-> So, as the greater thermal mass increases in temperature gradually, it's
-> loss to the surrounding air will be less than if it were heated
-> instantaneously. Over time the greater thermal mass will lose less heat to
-> its surroundings as it is absorbing more energy. It isn't really gaining
-> more, but has a similar result.
So, let's put what you said into context. A blade of grass has much
less mass than a chunk of asphalt. So, you appear to be saying, asphalt
will be cooler than grass when exposed to sunlight. I doubt that this
is really what you meant, but it does seem to be what you said.
-> Regards,
-> Steve
dow
J. Clarke
No, do the pushups. You really need to to get the full effect.
--
J. Clarke
> -> > No calculation is needed. If the two bodies equilibrate to
> unequal
> -> > temperatures, a heat engine can remove energy fromn them,
>
> -> Uh, tell us how to make this heat engine that works without
> -> transferring any energy from one reservoir to the other.
>
> Exactly. Any heat engine takes heat from a warmer reservoir and
> dumps
> some of it to a cooler one. If the reservoirs are at equal
> temperatures, it won't work.
And if they are not but there is no energy input then they will
equilibrate _through_ _the_ _heat_ _engine_ even if both are perfect
reflectors.
> -> Two isolated bodies of different colors in a perfectly reflective
> -> cavity is a different case from two bodied of different colors
> -> connected by a heat engine in a reflective cavity. You are
> taking
> the
> -> second case and claiming that it proves something about the
> first.
>
> They are different only if the heat engine is working and
> transferring
> heat. If the bodies are at equal temperatures, the engine can't
> transfer any heat, so its presence is irrelevant.
Post hoc ergo propter hoc. The conditions after the heat engine has
run for a bit don't define the conditions when it started running.
There is nothing in any law of thermodynamics that says that a heat
engine cannot run for a short time on energy stored in a reservoir.
> -> What I'm seeing is arm waving, not a calculation.
>
> What kind of calculation do you want?
Calculate the temperatures for your hypothetical situation.
> This is all standard physics. Look in any textbook.
OK, I'm looking in "Modern economics", which is most assuredly a
textbook, and not finding anything.
> Or ask a potter. When pots are being fired in a kiln, they can be
> seen
> by looking through a small hole in its door. When they are all at a
> uniform high temperature, red hot, they become virtually impossible
> to
> see, despite the fact that they may have been coated in glazes of
> very
> different colours.
You're assuming that the emissivity of the glazes is constant with
temperature.
> Compared with the dark-coloured ones, the
> light-coloured ones emit less light but reflect more, so the total
> brightnesses of the surfaces are equal. Equal temperatures
> correspond
> to equal radiation environments, regardless of colour.
>
> As I said. Standard physics.
So show us the calculation.
David Williams
-> equilibrate _through_ _the_ _heat_ _engine_ even if both are perfect
-> reflectors.
I didn't say that the two bodies are perfect reflectors. In fact, I
said they have different colours, which implies that they do absorb
some light. The walls of the box are perfect reflectors, so each of the
bodies is exposed to the radiation that has come from itself and from
the other body. In this radiation field, the two bodies equilibrate to
equal temperatures, even in the absence of the heat engine.
-> Calculate the temperatures for your hypothetical situation.
Okay. If one body has heat capacity H1, in any appropriate units such
as joules per degree Celsius, and the other body has heat capacity H2,
and if they start at temperatures T1 and T2, where T1 > T2, and if
their final equilibrium temperature is T, then the amount of heat that
will leave body 1 is H1(T1-T) and the amount that will be absorbed by
body 2 is H2(T-T2). These must be equal, so:
H1T1 - H1T = H2T - H2T2
so
H1T1 + H2T2 = T(H1 + H2)
so
T = (H1T1 + H2T2) / (H1 + H2)
Is that what you wanted? Does a bit of algebra make you happy?
-> > This is all standard physics. Look in any textbook.
-> OK, I'm looking in "Modern economics", which is most assuredly a
-> textbook, and not finding anything.
Now you're just being silly. In fact, this whole discussion lacks
merit, and is utterly off topic in this newsgroup. We should end it.
Now.
dow
J. Clarke
> -> And if they are not but there is no energy input then they will
> -> equilibrate _through_ _the_ _heat_ _engine_ even if both are
> perfect
> -> reflectors.
>
> I didn't say that the two bodies are perfect reflectors.
No, I was giving a worst-case example.
> In fact, I
> said they have different colours, which implies that they do absorb
> some light. The walls of the box are perfect reflectors, so each of
> the bodies is exposed to the radiation that has come from itself and
> from the other body. In this radiation field, the two bodies
> equilibrate to equal temperatures, even in the absence of the heat
> engine.
So if one body only absorbs light in a narrow band centered around the
peak of the blackbody curve at, say, 2000K, and the other only absorbs
light in a narrow band centered around the peak of the blackbody curve
at, say, 200K, they will somehow "equilibrate to equal temperatures"?
What is the mechanism?
When you use the word "color", you are really talking about "selective
absorbers", that have different absorptances at different frequencies.
> -> Calculate the temperatures for your hypothetical situation.
>
> Okay. If one body has heat capacity H1, in any appropriate units
> such
> as joules per degree Celsius, and the other body has heat capacity
> H2,
> and if they start at temperatures T1 and T2, where T1 > T2, and if
> their final equilibrium temperature is T, then the amount of heat
> that
> will leave body 1 is H1(T1-T) and the amount that will be absorbed
> by
> body 2 is H2(T-T2). These must be equal, so:
>
> H1T1 - H1T = H2T - H2T2
> so
> H1T1 + H2T2 = T(H1 + H2)
> so
> T = (H1T1 + H2T2) / (H1 + H2)
>
> Is that what you wanted? Does a bit of algebra make you happy?
Uh, that's the calculation for conductive heat transfer, not for
radiative with selective absorbers.
> -> > This is all standard physics. Look in any textbook.
>
> -> OK, I'm looking in "Modern economics", which is most assuredly a
> -> textbook, and not finding anything.
>
> Now you're just being silly. In fact, this whole discussion lacks
> merit, and is utterly off topic in this newsgroup. We should end it.
> Now.
Actually, the discussion of selective emitters and their properties is
very much _on_ topic in this newsgroup.
The reason that I used that example is that your "look in any
textbook" reveals a lack of familiarity with the coverage of heat
transfer in physics and engineering texts. Instead of looking in
_any_ textbook, one should be looking in one that is devoted to heat
transfer--Frank Kreith's "Principles of Heat Transfer" is one good one
that you can find used on Amazon for 4 bucks and shipping, however the
portions of it that are relevant to solar energy are also covered in
his "Principles of Solar Engineering" for about 30 bucks.
Note that to follow the discussion in either requires calculus.
David Williams
-> peak of the blackbody curve at, say, 2000K, and the other only absorbs
-> light in a narrow band centered around the peak of the blackbody curve
-> at, say, 200K, they will somehow "equilibrate to equal temperatures"?
-> What is the mechanism?
In that case, the rate of equilibration would be infinitessimal. But,
in reality, no two bodies are perfect absorbers or reflectors of
radiation in any frequency range. There will be some overlap, and the
rate of equilibration will be nonzero.
But, even in the first case, the equilibrium temperatures will be
equal. The fact that they take forever to get there doesn't alter that
fact.
-> Uh, that's the calculation for conductive heat transfer, not for
-> radiative with selective absorbers.
It works for both.
-> The reason that I used that example is that your "look in any
-> textbook" reveals a lack of familiarity with the coverage of heat
-> transfer in physics and engineering texts. Instead of looking in
-> _any_ textbook, one should be looking in one that is devoted to heat
-> transfer--Frank Kreith's "Principles of Heat Transfer" is one good one
-> that you can find used on Amazon for 4 bucks and shipping, however the
-> portions of it that are relevant to solar energy are also covered in
-> his "Principles of Solar Engineering" for about 30 bucks.
-> Note that to follow the discussion in either requires calculus.
-> --
-> --
-> --John
But getting involved in complex calculations is a waste of time when a
simple physical law, the Second Law of Thermodynamics, dictates the
answer. It's like people who invent "perpetual motion machines",
usually with many complicated unbalanced wheels, precessing gyros, and
so on, and claim that a full calculation of all the dynamics will prove
that the thing produces energy for ever. But the First Law of
Thermodynamics (conservation of energy) says that it can't, and really
that's the end of the story. Likewise, the Law of Conservation of
Angular Momentum shows that no machine that is entirely on the earth's
surface, with no coupling to anything outside it such as the moon's
gravity, can extract useful energy from the earth's rotation. As the
earth's rotation is slowed by the extraction of energy, angular
momentum would have to go someplace, and there is nowhere for it to go.
So such a machine cannot work, no matter how wondrous its design.
If a calculation suggests that two bodies in radiative equilibrium with
each other can be at different temperatures, then the calculation must
be wrong, even if it does involve calculus.
dow
RicodJour
>
> So? I used to *teach* calculus.
>
> But getting involved in complex calculations is a waste of time when a
> simple physical law, the Second Law of Thermodynamics, dictates the
> answer. It's like people who invent "perpetual motion machines",
> usually with many complicated unbalanced wheels, precessing gyros, and
> so on, and claim that a full calculation of all the dynamics will prove
> that the thing produces energy for ever. But the First Law of
> Thermodynamics (conservation of energy) says that it can't, and really
> that's the end of the story. Likewise, the Law of Conservation of
> Angular Momentum shows that no machine that is entirely on the earth's
> surface, with no coupling to anything outside it such as the moon's
> gravity, can extract useful energy from the earth's rotation. As the
> earth's rotation is slowed by the extraction of energy, angular
> momentum would have to go someplace, and there is nowhere for it to go.
> So such a machine cannot work, no matter how wondrous its design.
Several observations, a speculation and a comment.
Observations
- the Earth's rotational speed is slowing.
- tidal and wind effects fit into your "explanation" above, yet void
it.
- your sloppiness in your wording and in your explanations points to
your limited and sloppy understanding.
Speculation
- maybe there are Perpetual Motion Machines at work slowing down the
Earth. Damn them for not sharing!
Comment
- it's a good thing you are no longer teaching calculus to our youth.
It only takes one bad teacher to turn a kid off math.
R
J. Clarke
I have now determined to my satisfaction that you know absolutely
nothing of relevance about heat transfer and are unwilling to even try
to educate yourself.
That being the case,
<plonk>
David Williams
-> > simple physical law, the Second Law of Thermodynamics, dictates the
-> > answer. It's like people who invent "perpetual motion machines",
-> > usually with many complicated unbalanced wheels, precessing gyros, and
-> > so on, and claim that a full calculation of all the dynamics will prove
-> > that the thing produces energy for ever. But the First Law of
-> > Thermodynamics (conservation of energy) says that it can't, and really
-> > that's the end of the story. Likewise, the Law of Conservation of
-> > Angular Momentum shows that no machine that is entirely on the earth's
-> > surface, with no coupling to anything outside it such as the moon's
-> > gravity, can extract useful energy from the earth's rotation. As the
-> > earth's rotation is slowed by the extraction of energy, angular
-> > momentum would have to go someplace, and there is nowhere for it to go.
-> > So such a machine cannot work, no matter how wondrous its design.
-> Several observations, a speculation and a comment.
-> Observations
-> - the Earth's rotational speed is slowing.
-> - tidal and wind effects fit into your "explanation" above, yet void
-> it.
-> - your sloppiness in your wording and in your explanations points to
-> your limited and sloppy understanding.
-> Speculation
-> - maybe there are Perpetual Motion Machines at work slowing down the
-> Earth. Damn them for not sharing!
-> Comment
-> - it's a good thing you are no longer teaching calculus to our youth.
-> It only takes one bad teacher to turn a kid off math.
-> R
Tides slow the earth's rotation by coupling to the gravitational fields
of the moon and sun.
If you must criticize what I write, kindly read it first.
My students, some of whom I still know, held me in high esteem.
I won't trouble to read any more of your posts. You're an idiot.
dow
Steve
Yes, asphalt will initially be cooler, and take much longer to heat up than
a blade of grass. The blade of grass will reach equilbrium with its
surroundings rather quickly. The asphalt will take a long time to heat up
and hold a lot more heat than that blade of grass.
In the evening when it starts to cool down, the blade of grass will give off
its heat very quickly. The asphalt will continue giving off heat well into
the night. So... the grass will have less impact on night time temperatures
than asphalt.
Steve