# Cold Water

Hello ,

when i take out a cold bottle from the refrigerator , after a few seconds (lets say at room temperature) the bottle is surrounded by water.

the question is - why is it? where did the water come from ?
is it should happen with any cold body ?

(feel free to speak high phycis )

thank u !

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Nugatory
Mentor
There's some amount of water vapor floating around in the room air. The air next to the cold bottle is cooled by the bottle, and when it cools some of that water vapor condenses onto the bottle.

Any cold object will do the trick, but a bottle of water is particularly good at keeping its surface cool (because as the surface warms, water circulation brings more cold water from deep inside the bottle to the edge) so you may get a more pronounced effect with a bottle of water than, for example, an apple.

1 person
HallsofIvy
Homework Helper
Note that the amount of water that can be held in the air increases with the temperature of the air. Since the air is, as Nugatory says, cooled by the bottle the amount of water that it can hold is reduced. If the humidity (amount of water already in the air) it high the water will condense out of the air.

1 person
sophiecentaur
Gold Member
Note that the amount of water that can be held in the air increases with the temperature of the air. Since the air is, as Nugatory says, cooled by the bottle the amount of water that it can hold is reduced. If the humidity (amount of water already in the air) it high the water will condense out of the air.
That expression is a bit misleading but it's commonly used. In fact, it's all a matter of partial pressures. Air isn't a sponge (although that's what it seems). The maximum proportion of water vapour in the air is totally due to the vapour pressure at the ambient temperature. You would get exactly the same amount of water vapour in a container if the container were evacuated and then the pressure allowed to increase as water evaporates off a water surface. The equilibrium situation would always involve 'saturated' air (there- I've done it myself!)

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so I have another question - what makes the water act like a gas ? I know that the evaporation temp. at room pressure is ~ 100 C , so if the temperture is < 100 and the pressure is ~ 1 atm why the water are gas?

thank you

sophiecentaur
Gold Member
so I have another question - what makes the water act like a gas ? I know that the evaporation temp. at room pressure is ~ 100 C , so if the temperture is < 100 and the pressure is ~ 1 atm why the water are gas?

thank you
There is still a pressure of vapour from the water surface at temperatures less than 100C. The reason that boiling occurs is that the vapour pressure at 100C is equal to atmospheric. Up on a mountain top, water will boil rapidly in the low 90s (Hopeless for cooking) but, in a pressure cooker, the water will boil at a higher temperature.
Below boiling point, there is a constant exchange of molecules of and onto the surface. Don't confuse the equilibrium situation (in closed box after a long time) with what happens when there is a constant supply of fresh air over the surface.

so lets say I take a glass of water and put it in a closed box ( vacccum)- there will be no vapours?

sophiecentaur