Water, paper towel and energy

  1. tony873004

    tony873004 1,588
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    If you dip a paper towel into water, the water absorbs up the paper towel. These molecules are gaining height, and hence mgh is increasing. Where does the energy come from to lift the water molecules?
     
  2. jcsd
  3. From the energy required to manufacture the paper.
     
  4. tony873004

    tony873004 1,588
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    Gold Member

  5. Andy Resnick

    Andy Resnick 6,019
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    Here's a twist- what happens if you take away gravity? The answer is not so simple, and relates to how to grow food in space.
     
  6. So, if the energy required to lift the water through capillary action, is coming from the
    inter-molecular forces, then why aren't these forces being 'used up' very slightly as they convert their energy into the gaining of height by the water molecules?
     
  7. The forces aren't 'used up'. Onlly energy is used up. you can get energy out of water and a paper towel by letting the towel get wet. you have to spend energy to get the water out of the towel again. (pressing or heating)
     
  8. Andy Resnick

    Andy Resnick 6,019
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    Education Advisor

    Capillary rise coverts surface energy into gravitational potential energy. When the liquid stops rising, the increase in potential energy is balanced by the loss of surface energy from wetting.
     
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