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Viscosity of two different liquids

  1. Apr 2, 2009 #1
    I was just wondering. Say you have two different liquid with two different viscosities (water and oil, etc). If you have them in two different containers, and having the same amount in each container, say 500 mL. You heat them both to some temperature, say 100 F. Since liquid expands when it is heated, would you expect the liquid with the lower viscosity to rise higher in the container (ex. water) or am I thinking of this wrong?

  2. jcsd
  3. Apr 2, 2009 #2


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    I think you might be phrasing it wrong. Don't you mean density rather than viscosity?

    Anyway, water and oil don't mix, and have different densities (water is heavier). Different fluids can also have different thermal expansion coefficients. So, you can have two immiscible fluids A and B, where A is lighter than B at one temperature and heavier than B at another. In fact, that's how "lava lamps" work.

    If the two fluids are miscible then they'll act as a single fluid; heating or cooling the liquid won't separate them.
  4. Apr 3, 2009 #3
    Let me clarify. I do mean viscosity. The water and oil was just an example. I'm saying any two liquids, like maple syrup and honey to simplify. But they are NOT mixed together. So you have 500 mL of syrup in a beaker and another beaker with 500mL of honey. Im saying that since the viscosity of these two liquids is different what would happen if you heat both beakers to 100F? Would the level of the liquid with the lower viscosity rise higher? (Although the rise may be too small to notice)
  5. Apr 3, 2009 #4


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    "Since the viscosity is different" .. so?

    Viscosity has little to do with density. Viscosity is related to the inter-molecular forces, whereas density is inter-molecular distance. E.g. Water with starch in it has much higher viscosity than pure water, but about the same density.

    So my answer would be then, that you simply can't predict the changes in density from the viscosity. I don't see any reason to think that one could.
  6. Apr 3, 2009 #5


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    You might be able to see a correlation between viscosity and coefficient of thermal expansion for closely related compounds, say, two examples of a certain polymer with slightly differing molecular weights.
  7. Apr 4, 2009 #6
    For many liquids and temperature ranges density reduces with temperature as does viscosity so there may be an as yet to be discovered relationship.
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