Talk:Relative humidity
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Totally incorrect. The relative humidity has absolutley nothing to do with soluability of water in air - it is governed by the partial pressures. Furthermore we need to clarify units. If absolute humidity is to be expressed as a percentage - then a percentage of what verses what? grams verses m^3? That makes no sense! Volume H2O verses volume of air? How does temperature effect this? Mass of H2O verses mass of air?
Clearly there is a degree of confusion here.
Terrell Larson (minor update to link in my log in)
A very helpful article! what I found missing here was reference to typical values of relative humidity, e.g. perhaps is it 0% only in the desert? And is it 100% in a rainforest? etc.
Judging by the appearance of the graph I don't see how relative humidity could be inversely proportional to temperature. The current graph would have to be flipped about the vertical. The graph appears to be exponential, but I would appreciate if somebody in the field or in the know would write the equation(s) that relate relative humidity (dew point etc) and temperature.
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[edit] Condensed water on car window - heating or cooling?
Especially in winter time it's common for car windows to get a thick layer of condensed water vapor on them. My brother and I were aguing what's better to do in that situation: he said it's better to put on the heating, so that the windows start to warm up and the car's interior can hold up more water vapor. I argued that cooling the car will bring the whole system (outside - window - inside) in a temperature equilibrium, thus the water vapor has no specific preferred place to condensate.
What whould you say is better? Heating or cooling? --Abdull 6 July 2005 09:55 (UTC)
- Heat the windshield to bring its temperature up to above the dew point of the car's interior. Vsmith 6 July 2005 15:47 (UTC)
- I agree absolutely with Vsmith, but if your heater doesn't work, open the windows to remove the (extra human-made) water vapour from the car-- assuming the outside air is dry winter air.82.93.133.130 20:14, 9 November 2006 (UTC)
This comment of units is bit funny - if it's percentage then the units are the same, i.e. the present mass of the water (vapour) in relation to the mass of the water (vapour) in the saturated air. One thing bothers me though. It says there, that in saturated air the water won't lose its mass - I think I know what the author meant, but it may seem to somebody, that water vapours because it actually loses it's mass (literally, physically), which is not true.
[edit] Not Completly Accurate
The verbiage in this article leads the reader to believe that solubility plays a role in relative humidity. This is not the case.
Relative humidity has noting to do with solubility of water in air. This statement must be removed: The warmer air is, the more water vapor it can "hold."
Air does not "hold" water.
Furthermore:
The term Dew Point needs to be better articulated. Dew Point Temperature and Dew Point Pressure need to be distinguished in the discussion of Relative Humidity.
The Relative Humidity of a gas is a function of not only the absolute pressure but also temperature of the gas.
- So for simplicity's sake, should we tell the reader right off that we're assuming we're at sea level-760mmHg?? Gaviidae 22:11, 21 November 2006 (UTC)
As for the condensation problem in a vehicle: What is going on? When the water content in the cabin air inside the vehicle increases the dew point temperature of this water/air mixture also increases. When this gas mixture contacts a surface (such as the window) which is below the dew point temperature of the mixture condensation will occur.
What is the "best" thing to do? Do both. Remove water vapor from the air by operating the air conditioner and heat the internal surfaces of the cabin by turning on the heater so they remain above the dew point temperature of the cabin air.
In practice turning on the air conditioner will immediatly reduce window condensation because this action will remove water from the cabin air inside the vehicle. Turning on the heater alone will also reduce condensation but not as readily because the heater must heat the cabin air and then this thermal energy needs to be transfered to the internal surfaces of the vehicle. This is a slower process than cooling air with the vehicles A/C.
[edit] Thanks for the changes...
I like some of the changes users have made to the intro, overall the article is shaping up nicely. Some changes however:
The following verbiage does not make sense ...under conditions of vapor saturation at a given temperature (see: common misconceptions below). and has been removed.
I have removed the incorrect phrase: more technically more technically than what? It does not seem to fit here.
I noticed the definition was reverted back to the concept of air-holding water for relative humidity - PLEASE avoid explaining the concept of relative humidity in these terms. This is absolutely incorrect.
Also removed the reference Technical definition and replaced it only with Definition. The adjective technical implies there are other definitions to relative humidity, this being the technical one. Infact this is the definition of relative humidity.
- I've always been told also that warmer air "holds"more moisture-- that, air pressure being the same, more water will stay in droplet form in warmer air than colder air. If I have 2 beakers at room temperature, and they both have the same % of water relative to air volume, and I heat one beaker, there will be less condensation than in the other... but now of course I've changed the pressure in that beaker... whoops. : )
- But my question is with this sentence: Water vapor is a lighter gas than air at the same temperature, so humid air will tend to rise by natural convection. Huh? Why do clouds have to "rain" to get over the mountains (old school lesson, I know)? Isn't the windy side of the mountain range getting more yearly rainfall than the leeward side?? because the clouds are too heavy (or dense) to rise over the mountaintops?? The article didn't make this clearer, esp not this sentence. Humid air is "lighter" (less dense?) than dry air?? Gaviidae 20:24, 9 November 2006 (UTC)
Ok, this is what I got from How Stuff Works [1]: Absolute humidity is the mass of water vapor divided by the mass of dry air in a volume of air at a given temperature. The hotter the air is, the more water it can contain. Relative humidity is the ratio of the current absolute humidity to the highest possible absolute humidity (which depends on the current air temperature). A reading of 100 percent relative humidity means that the air is totally saturated with water vapor and cannot hold any more, creating the possibility of rain... Since HSW is also just another website, how does this definition compare to say, a real college textbook? Why doesn't it mention saturation and air pressure in mb? Gaviidae 20:29, 9 November 2006 (UTC)
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- Me again-- HSW not well written. Found two better sources, but I'm afraid to use one on Wikipedia because I dunno what gsu.edu IS-- I only found their database, great for basic stuff of all sorts http://hyperphysics.phy-astr.gsu.edu/hbase/ and the humidity stuff at http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/relhum.html and also friendly meteorologist http://www.shorstmeyer.com/wxfaqs/humidity/humidity.html
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- The way they put it (hyperphysics good for diagrams, Shorstmeyer good for basic energy concepts), air is air and liquid will enter air when liquid molecules get enough energy to fly and be free and all that. So the reason air doesn't "hold" water is that the water holds itself with its energy. Warmer air CAN HAVE more moisture because the warmth in the air is energy that, if harnessed by any liquid water laying around, is used to launch water molecules into the air. Cool. Colder air has less energy, and as water molecules in the air bounce into and off from colder molecules, they lose their kinetic energy and can no longer fight hydrogen bonds and van der waals-- forces that keep water molecules together as water. Wow. Gaviidae 22:08, 21 November 2006 (UTC)
[edit] Lack of citations
Hi all. This article fails to cite its sources per WP:REF. I therefore added the tag for this on the article page. Not citing sources is substandard for Wikipedia articles. Moreover, the recent revert war may have thereby been avoided. CyberAnth 18:12, 8 October 2006 (UTC)
[edit] Wet cities and dry cities
Is there anywhere on the internet where I can compare relative humidity in different places in the world, perhaps using a map or table or something? —Lagalag 19:49, 10 November 2006 (UTC)
- I did not look for tables with cities, but as I was looking for better explanations of humidity, I found this meteorologist's site,and he does mention places with highest recorded dew point temps-- http://www.shorstmeyer.com/wxfaqs/humidity/humidity.html Gaviidae 22:01, 21 November 2006 (UTC)
