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Why does viscosity change with temperature?

  1. Apr 6, 2006 #1
    Does anybody know why viscosity changes with temperature?

    I'm expected to do a short explanation or suggestion for my homework of why this happens but to be honest I'm not sure. :confused:

    The only reason I can think of is higher temperature means more energy therefore less internal resistance to movement but that is quite a poor explanation.

    Could anybody explain to me why viscosity decreases with temperature increase?
     
  2. jcsd
  3. Apr 6, 2006 #2

    berkeman

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    Staff: Mentor

    What have you found so far with your google search?
     
  4. Apr 6, 2006 #3
    "When a fluid is heated, the particles within the fluid gain kinetic energy, and will be more able to overcome the intermolecular attraction forces within the fluid."

    I think this will be enough actually, but I'm not sure why the decrease is an exponential decay.
     
  5. Apr 6, 2006 #4

    FredGarvin

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    You have answered only half of the real question. Can you explain why the viscosity of a gas increases with temperature while viscosity of a liquid decreases with temperature? They are both fluids.
     
  6. Apr 6, 2006 #5
    I meant just liquids.
     
  7. Apr 22, 2010 #6
    viscosity is dependant on both momentum interchange and cohesive forces. In gases, momentum interchange is dorminant..as the temp. of the gas is raised, particles gain kinetic energy and therefore on collision, there's a greater transfer of momentum which results in the inrease in viscosity. In liquids, cohesive forces dorminate....when temperatures are raised, particles gain energy enouigh to overcome the intermolecular forces of attraction thus decreasing the cohesive forces. Decrease in these cohesive forces reduces the viscosity in the liquid.
     
  8. Apr 22, 2010 #7
    does that help ?
     
  9. Apr 22, 2010 #8

    berkeman

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    It probably doesn't help Macca604, since this thread is 4 years old. But it may help others who search for this subject.

    Welcome to the PF.
     
  10. Apr 23, 2010 #9
    .....4 what ? damn!
     
  11. Apr 23, 2010 #10

    berkeman

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    For which? The necropost miss, or that fact that it might help others in the future?
     
  12. Apr 24, 2010 #11
    ..the necropost miss.
     
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