# How do clothes get dry from being outside or on radiators?

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I understand how water molecules become gaseous when heated to 100 degrees, but there is no point in drying when the clothes would get that hot, so how does the water leave the clothes?

In: Physics

Partial pressure difference. There’s more water in your clothes than in the air surrounding it; water molecules will leave the clothes until the pressure is equalized. Water evaporates from seas/lakes/rivers/oceans at all temperatures, not just at 100C. Adding heat just adds energy that makes it easier for the molecules to detach from each other. Have you noticed how it takes longer to dry your clothes when the day is humid, like after it rains, when there’s more water in the air already.

At 100C and normal preasure the water will want to be at the same pressure as air, meaning it could replace the air completely and stay as a gas.

At lower temperatures it can only fill a part of the air, “a part of the pressure”. That’s why its not boiling, because it cannot form gas inside the liquid, only on the surface.

There’s a limit to which air can carry water in it. And this is usually expressed by its temperature. So the amount of water air can carry depends on the temperature of the air. Now air is a composition of many gases. Oxygen, nitrogen etc all of them are in their gaseous forms. All of them exert some partial pressure to sum up to atmospheric pressure(at sea level) and more a particular gas is in the air, more partial pressure it exerts. And this should include water as well. At normal pressure of 1atm, water boils at 100 degrees Celsius. But when you take water at a lower pressure, if boils at lower temperatures and you can see this in regions of higher altitudes where you can find water boiling at 70 degree centigrade. Similarly, at room temperature, there exists a pressure value that water can boil at which is lower than atmospheric pressure. And when you start with dry air and put water in it, slowly the water will start to evaporate until the partial pressure of water reaches the pressure water will start to boil. So, to dry clothes there are several factors that’ll help, you need to increase the airs temperature so as to increase its water carrying capacity, increase air flow to facilitate the boiling process or supply it with dehumidified air. Radiators supply heated air and if it’s put outside, the air velocity will help with the boiling of air and if it’s under the sun, it’ll keep the temperatures up.

Basically because water likes to move from a wet place to a dry place…

if the air around the clothes is drier than the clothes water will move from wet to dry.

its why its horrible to try to dry your clothes on a hot humid day( it’s also why it’s so hard to sweat properly )

if you put your clothes on an outside dryer the winds will blow through them bringing in drier air and thus encourage more movement of wet to dry.

when the weather is hot( but not humid) the air expands( or rather the molecules) and thus there is more space to absorb more water, hence the air will be even drier.