# How does something just ‘dry’ against the air?

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For example clothing on a washing line. How does it dry up? What makes the water get out of the clothes? Where does the water go?

Also a different question but still on the same topic; what is the reason that some materials such as glass don’t absorb water, but materials like paper do?

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Heat is just a human concept for the kinetic motion of the molecules of an object. When you hear water up past 100C the molecules are moving so fast that they are not able to stay together and become vapor. However, when water is not that hot, *some* of the molecules of water *do* move fast enough to break free. You can see this when you leave an open container of water overnight and it evaporates slightly. The less humid the air surrounding the water is, the easier it is for that water to evaporate into the atmosphere and dry up the container or soaked object.

The reason paper soaks up water is because paper has microscopic spaces between each cellulose fiber that’s big enough for water to seep through. Glass has no pores that are big enough for water so it does not absorb water.

Air is a mixture of gases: nitrogen, air, some other stuff….and water. The water in air is in a gas state and is called water vapor.

The amount of water vapor that can be held by air depends on the temperature and the amount of water vapor already on the air.

Air in the desert is hot and dry (very little water vapor already in the air, and the air can take more water.). Air in a spring rainstorm is cold and wet or clammy (air is almost “full” of water and can’t hold any more.)

If you put a wet sheet out in hot dry desert air, the air will absorb the water in the sheets as a gas, and the sheet will dry quickly. If you put a wet sheet out in a spring rainstorm, it won’t dry (even if it’s shielded from the rain) because the air can’t accept any more water vapor.

As far as other materials soaking up liquid water – that’s just a function of how much space there is in between the solid bits of material and whether the structure of the solid allows the water in.

A sponge has lots of empty space (holes) between the solid bits, and those holes are all connected….so a sponge will soak up lots of liquid.

Glass has no holes between the solid bits…:so it won’t soak up any liquid. Glass is impervious.

Wood and paper also have lots of space in their internal structure and can soak up a fair amount of water.