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Changes in Water Weight

  1. Feb 9, 2012 #1
    I have something I need cleared up and looking for some calculation help. I know that water changes density with temperature but does it change due to lack of gravity when the moon is close? So to clear things up I guess I need to know what and how thoes changes will affect the weight of water. Also the how much does the atmospere pressure affect it/

    If I had 500grams of water in a bottle how much would it weight at a temperature change or pressure change? this isnt a homework question just something I am arguing with a friend about.

    Thank you
     
  2. jcsd
  3. Feb 9, 2012 #2
    No, it does not lose mass. Ice is less dense because the molecular structure of ice takes up more space than the molecular structure of liquid water. If you started with 500 grams of liquid water it would have a volume of 500 milliliters. After freezing it would have a volume of roughly 550 milliliters. It would still have a mass of 500 grams.
     
  4. Feb 9, 2012 #3
    Yes I am clear on this but if the temperature changes in the water will the weight change?
    If I have 500grams of water at 70F do I still have 500 grams at 90F?
     
  5. Feb 9, 2012 #4
    A table of the density of water at various temperatures is given here:

    http://en.wikipedia.org/wiki/Density_of_water#Density_of_water_and_ice

    Follow the increasing density progression in the chart and note the change starting around zero degrees...


    The effects of gravity on matter are extremely tiny, almost inconsequential, in everyday circumstances. In extreme gravity, electron degeneracy pressure is a major effect as in
    neutron stars.
     
  6. Feb 9, 2012 #5

    davenn

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    yes you do. thats just the opposite of what Subductionzon said in his post where he dropped the temp rather than increased the temp of the water

    density isnt so much related to weight (mass) as it is to weight per unit volume. eg.

    I have 1kg of aluminuim and 1kg of lead. lead is more dense than aluminuim and as a result its volume is going to be smaller than that of 1 kg of aluminium

    Dave
     
    Last edited: Feb 9, 2012
  7. Feb 10, 2012 #6
    using the density table I would assume that If i had 500ml of water in a bottle at 4C then I would have 500 X 0.9999720= 499.986 grams of water

    at 22C I would have 500 X .9977735 = 498.886775 grams of water

    Does this sound correct?
     
  8. Feb 10, 2012 #7
    Yes, at a set Volume the Mass of the water in that Volume will vary with temperature and you are going about it correctly. Now your original question asked what would happen when you had a set volume of water what would happen to that waters mass if you changed the temperature or pressure. In that case, since you already had a set amount of water its mass would not change. But its volume would.

    As a slight aside. I know they have a different definition of a gram now but wasn't it originally defined as the mass of one cubic centimeter, or one milliliter of water? At 0 C of course.

    ETA: Never mind, it was. And later defined as the same volume at 4 C.
     
  9. Feb 10, 2012 #8
    I see where the confusion was I guess i didnt explain what I was trying to do in my first point. But you have answered what I was looking for.

    Thank you to everyone who replied!
     
  10. Feb 11, 2012 #9
    Does anyone know where or how I could calculate the change during pressure changes?
     
  11. Feb 11, 2012 #10
    Change of what?
     
  12. Feb 11, 2012 #11
    The mass of the water
     
  13. Feb 11, 2012 #12

    DaveC426913

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    Pressure changes do not affect the mass of the water. You are still confused.

    The only way the mass of the water will change is if some of the water leaves the container. To do this, the container must be open. If the container is open then expansion will not result in a pressure buildup.

    If you wish the volume to remain the same and instead let the pressure build up, then you will need a closed container and no water will escape, thus the mass of the water will not change.
     
  14. Feb 11, 2012 #13
    Doesn't it change the volume? If I fill a bottle with water at 22degC and atm. Pressure at 14.7 psi, say I have 500grams of water in the container. Then I empty the container change pressue to 15.7psi and refill it will it remain the same. Say a plastic bottle.
     
  15. Feb 11, 2012 #14

    DaveC426913

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    Change the pressure of what? You've emptied the bottle.
     
  16. Feb 12, 2012 #15

    Ok i will try this again.....Let say I have an empty plastic bottle and I want to fill it with water to see how many grams it weighs. So I do this at 70deg F. and 14.7psi atmosphere pressure(no cap) take my measurement and I get 500grams......Now I record my measurement and empty the bottle. I already know that If i increase the temperature of the water and refill it the measurement will be reduced due to the density of the water so Im only going to increase the atmospere pressure to 15.7psi. So now that my temperature is the same and the only change is to the atmosphere pressure by 1 psi, and I do the same test will I still find that I get a measurement of 500 grams?
     
  17. Feb 12, 2012 #16

    DaveC426913

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    No, you will get a number very slightly larger than 500 grams. Water is nearly incompressible, but not completely so. An increase in pressure - especially, yours which is less than 10% - will have a vanishingly tiny impact - though not zero - on the density of the water. Since the density is greater, but the volume is the same, there is will slightly more water in the bottle than before.

    Note that, since you are pressurizing the entire chamber that the bottle is in, bottle is in equilibrium. The plastic bottle does not have to be capped, nor does it expand.
     
    Last edited: Feb 12, 2012
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