water

Discussion in 'General Science & Technology' started by citys4, Jul 9, 2010.

Thread Status:
Not open for further replies.
  1. citys4 Registered Senior Member

    Messages:
    15
    i have a few questions first why dose water evaporate?
    second i was thinking if i put water by the windows will it keep my house cooler since water takes longer to heat up and cool down it?
    thx
     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. Kernl Sandrs Registered Senior Member

    Messages:
    645
    When water evaporates, it's the molecules bouncing around, and then they get enough velocity to escape. Or something like that, I'm going off what I remember. I don't want to look it up just as easily as you could...



    No, it will not.

    Takes longer than what?
     
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. Fraggle Rocker Staff Member

    Messages:
    24,690
    First, remember that in a liquid, all the molecules are moving around in all directions, more-or-less at random. Now imagine that a body of water is sitting out in the open, exposed to the air.

    A unit volume of air at any given temperature and pressure has a capacity to carry a certain number of water molecules. If it actually contains that number of water molecules, this is the definition of 100 percent relative humidity.

    Now if one of those water molecules right up at the surface happens to be moving upward, it will rise slightly above the surface of the water into the lowest layer of the air. But the air already has as many water molecules as it can hold, so it can't stay, and will fall back down.

    But if the air is not at 100% relative humidity, that means that it has the capacity to carry more water molecules than it currently has. So when that water molecule breaches the surface and enters the air, it is welcome to stay there. This is the process we call evaporation.

    If the temperature drops or the air pressure increases, then the air cannot hold quite as many water molecules as it could before. If it's already at 100% relative humidity, it will eject some of them and they will fall back down to earth. This is the process we call rain.
    You would have to build a layer of water that completely covers the windows. Then you would, in effect, be using water as insulation. That would stop the heat transfer from the outside air, through the glass, to the inside air.

    That's not very practical because water is heavy and sloppy to work with, and if the window breaks you end up with a big mess. Also, looking through a layer of water would make your view a little weird.

    Instead they just use air, which is an even better insulator than water. They build a window with two panes of glass, and the space between them is sealed so the air is trapped and can't circulate to be replaced by warmer air from outdoors. Double-pane windows are quite common these days and many newly-built houses have them. They lower your heating and air-conditioning bills considerably because you no longer have heat transfer through the glass. We just had them retrofitted into our house.
     
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. citys4 Registered Senior Member

    Messages:
    15
    thx so i should keep my windows closed it will be cooler than if windows opened
     
  8. Nesm Registered Senior Member

    Messages:
    125
    Why would water be ejected from the air when humidity is at 100%? It would seem that if the air has no capacity for the further uptake of water, then that condition would be maintained indefinitely.
     
  9. Nesm Registered Senior Member

    Messages:
    125
    Missed that, sorry. Question answered.
     
  10. sifreak21 Valued Senior Member

    Messages:
    1,671
    love water one of the single most interesting physics defying elements
     
  11. Skeptical Registered Senior Member

    Messages:
    1,449
    To citys4

    If you can build a picture in your mind of the movement of gas and liquid molecules, it may help your understanding.

    Imagine gas molecules as bouncing around and off everything they meet. Like a billion ping pong balls bouncing - both off the floor and off each other.

    Now imagine the movement of liquid (water) molecules. Instead of bouncing, it is like a tank of moving ping pong balls that simply roll around. Imagine the tank shaking, to keep those balls rolling around in the tank and around each other.

    It is energy that makes molecules behave like that. Putting more energy in is like shaking the tank harder. If the tank shakes enough, some of the balls will pop out of the tank, and join the ping pong balls bouncing off each other in the air.

    That is, more or less, what happens when water molecules evaporate. Energy is added, which makes them move faster, and some will pop into the air, and become part of the air. When energy is removed, and the air cools, the water molecules move more slowly and eventually fall back down. This is called rain.

    If enough energy is removed, it is like stopping the tank shaking. The balls will settle down and be (mostly) still. When water molecules do this, they freeze, forming ice.
     
  12. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

    Messages:
    19,252
    Physics defying?

    Please Register or Log in to view the hidden image!

     
  13. Skeptical Registered Senior Member

    Messages:
    1,449
    Call it apparently defying physics. Where else do you see a liquid expanding as it cools?
     
  14. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

    Messages:
    19,252
  15. phlogistician Banned Banned

    Messages:
    10,342
    Nope. It just doesn't behave the way non-scientists expect it to.

    But herein is the difference. Scentists try and remove their expectations from their observations, so as to not taint the results.

    Woowoos however start making up all manner of ridiculous explanations to explain why reality doesn't match up with their expectations.
     
  16. citys4 Registered Senior Member

    Messages:
    15
    thx for the answer
     
  17. sifreak21 Valued Senior Member

    Messages:
    1,671
    well no i guess not but its the only element that expands when frozen and contracts when hot. its the most powerful eroder? cant think of the word im looking for..
     
  18. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

    Messages:
    19,252
    No it isn't.

    Read the linked thread: it dispells a lot of myths about water.
     
  19. spidergoat pubic diorama Valued Senior Member

    Messages:
    54,036
    Yes, if you keep water evaporating by your window, it will cool your house. An elaboration on this effect is called a swamp cooler, very common in desert climates instead of air conditioning.
     
  20. Fraggle Rocker Staff Member

    Messages:
    24,690
    Water is not an element; it's a compound of two elements: hydrogen and oxygen.
    We had those in our house in Tucson in the 1950s, before home air conditioning became affordable. They are utterly worthless. You're lucky if they drop the temperature five degrees Fahrenheit.
     
  21. spidergoat pubic diorama Valued Senior Member

    Messages:
    54,036
    Not necessarily. My friend in the desert uses one and on a 90 degree day, it's about 80 degrees inside. Of couse it's not as effective as an air conditioner, but it does use far less energy.
     
  22. Skeptical Registered Senior Member

    Messages:
    1,449
    Water based cooling systems depend on the design. A crude version can be almost worthless. A well designed and well installed system can be most effective.

    What is needed is lots of evaporation, requiring large surface area, and the set up to permit the heat for evaporation to be drawn from within the house to be cooled.

    An early crude system was used in the days of the British Raj in India. Servants would carry buckets of water onto the roof of the 'bosses' house and tip the water over its surface. As it evaporated, it would cool the entire house. Crude, but effective.
     
  23. Fraggle Rocker Staff Member

    Messages:
    24,690
    I consider an 80-degree (27C) house child abuse. Besides, it was 105 in Tucson, so at best it was 95 indoors. That really was child abuse. I never forgave them for seven miserable years in that shit-hole.
     
Thread Status:
Not open for further replies.

Share This Page